美军标 18240

INCH-POUND

MIL-DTL-18240F

2 JUNE 1997

SUPERSEDING

MIL-F-18240E

1 DECEMBER 1989

DETAIL SPECIFICATION

FASTENER ELEMENT, SELF-LOCKING, THREADED FASTENER, 250°F MAXIMUM

This specification is approved for use by all Departments and Agencies of the Department of

Defense.

1. SCOPE

1.1 Scope. This specification defines the requirements for self-locking elements for use in

externally threaded fasteners such as bolts and screws to be used in fasteners with either UNC,

UNJC, UNF, UNJF, UNRC or UNRF threads and where the temperatures will not exceed 250°F.

1.2 Classification. This specification includes three types of self-locking elements as follows:

Type N . . . . . Plug/Pellet

Type L . . . . . Strip

Type P . . . . . Patch

Beneficial comments (recommendations, additions, deletions) and any pertinent data which

may be of use in improving this document should be addressed to: Commander, Naval Air

Warfare Center Aircraft Division, Code 414100B120-3, Highway 547, Lakehurst, NJ

08733-5100, by using the Standardization Document Improvement Proposal (DD Form

1426) appearing at the end of this document or by letter.

AMSC N/A FSC 53GP.

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.

MIL-DTL-18240F

2. APPLICABLE DOCUMENTS

2.1 General. The documents listed in this section are specified in sections 3 and 4 of this

specification. This section does not include documents cited in other sections of this specification or

recommended for additional information or as examples. While every effort has been made to ensure

the completeness of this list, document users are cautioned that they must meet all specified

requirements documents cited in sections 3 and 4 of this specification, whether or not they are listed.

.

2.2 Government document.

2.2.1 Specifications Standards and handbooks. The following specifications, standards, and

handbooks form a part of this document to the extent specified herein. Unless otherwise

specified, the issues of these documents are those listed in the issue of the Department of Defense

Index of Specification and Standards (DODISS) and supplement thereto, cited in the solicitation

(see 6.2).

SPECIFICATIONS

FEDERAL

QQ-P-416

GGG-W-686

-

-

Plating, Cadmium (Electrodeposited).

Wrench, Torque, Unidirectional.

DEPARTMENT OF DEFENSE

MIL-S-7742

MIL-S-8879

STANDARDS

FEDERAL

FED-STD-H28/2-Screw Threads Standards for Federal Services Section 2

Unified inch Screw Threads UN and UNR Thread Forms

-

-

Screw Threads, Standard, Optimum Selected Series: General

Specification for

Screw Threads, Controlled Radius Root with Increased Minor

Diameter, General Specification for.

DEPARTMENT OF DEFENSE

MIL-STD-1312-7-

MS15981

Fastener, Test Methods, Method 7, Vibration

- Fasteners, Externally Threaded, Self-locking, Design and

Usage Limitations For

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MIL-DTL-18240F

AIR FORCE - NAVY AERONAUTICAL

AN 3 THRU AN 20- Bolt, Machine, Aircraft.

(Unless otherwise indicated, copies of the above specifications, standards, and handbooks are

available from the Standardization Document Order Desk, 700 Robbins Avenue, Building 4D,

Philadelphia, PA 19111-5094.)

2.2.2 Non-Government publications. The following documents form a part of this document

to the extent specified herein. Unless otherwise specified, the issues of the documents which are

DoD adopted shall be those listed in the issue of the DoDISS cited in the solicitation. Unless

otherwise specified, the issues of documents not listed in the DODISS are the issue of the

documents cited in the solicitation (see 6.2).

AMERICAN SOCIETY FOR QUALITY CONTROL (ASQC)

ASQC Z1.4- Sampling Procedures and Tables for Inspection by Attributes

(Application for copies should be addressed to AMERICAN SOCIETY FOR QUALITY

CONTROL, P.O. Box 3005, 611 E Wisconsin Ave, Milwaukee, WI 53201-4606)

AMERICAN SOCIETY OF MECHANICAL ENGINEERS

ASME B1.1- Unified Inch Screw Threads (UN and UNR Thread Form) (DoD adopted)

(Application for copies should be addressed to American Society of Mechanical Engineers

(ASME), 22 Law Drive, P.O. Box 2900, Fairfield NJ 07007-2900)

NATIONAL AEROSPACE STANDARDS (NAS)

NAS 600 THRU NAS 606- Screw, Machine, Aircraft, Pan Head, Cruciform Recess,

Full Threaded, Alloy Steel. (DoD adopted)

(Application for copies should be addressed to the Aerospace Industries Association of

America, Inc., 1250 Eye Street, N.W., Washington, DC 20005.)

AMERICAN SOCIETY FOR TESTING AND MATERIALS

ASTM D1535-Standard Practice for Specifying Color By The Munsell

System

(Application for copies should be addressed to the American Society for Testing and

Materials, 100 Barr Harbor Drive, W. Conshohocken, PA (19428-2959).

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MIL-DTL-18240F

2.3 Order of precedence. In the event of a conflict between the text of this document and

the references cited herein (except for related associated specifications or specification sheets), the

text of this document shall take precedence. Nothing in this document, however, supersedes

applicable laws and regulations unless a specific exemption has been obtained.

3. REQUIREMENTS

3.1 Qualification. The self-locking elements furnished under this specification shall be

products which are authorized by the qualifying activity for listing on the applicable qualified

products list (QPL) before contract award (see 4.2 and 6.3).

3.1.1 Extent of qualification. Qualification approval of external self-locking element in UNF

or UNJC external thread constitutes approval of external self-locking element in UNC, UNJC,

UNF, UNJF, UNRC, or UNRF external thread of the same diameter.

3.2 Design. The self-locking element design shall conform to the types illustrated on

figure 1 and MS15981.

3.2.1 Dimensions. The self-locking element dimensions shall be as specified in table I,

table IA, and figure 1. In cases of dimensional conflict, the dimensions of table I, table IA and

figure 1 shall take precedence over those identified in MS15981.

3.3 Performance characteristics.

3.3.1 Torque. The self-locking fastener shall conform to the torque test as specified in 4.4.2.

3.3.2 High temperature torque. The self-locking fastener shall conform to the high

temperature torque test in 4.4.3.

3.3.3 Off prevailing torque at maximum temperature. The self-locking fastener shall meet

the off minimum prevailing torque values specified in table II at maximum temperature when

tested in accordance with 4.4.4.

3.3.4 Vibration. The self-locking fastener shall be subjected to and pass the vibration test

for 30,000 cycles as specified in 4.4.5. For qualification purposes, the activity responsible for

qualification may waive the vibration requirement for thread sizes greater than .500 inch provided

the .500 inch thread size having the same type locking element has passed the vibration test. The

vibration test is not required for thread sizes below .190.

3.4 Reusability. The self- locking fastener shall be capable of 5 seated cycles without

damage to either the nut or bolt threads (see 4.4.2d through f and 4.4.6).

3.5 Identification.

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MIL-DTL-18240F

3.5.1 Self-locking element. The self-locking element shall be identified by color code as

identified in ASTM D1535 and in table VIII.

3.5.2 Color. Each manufacturer of the products specified herein shall color code their

self-locking elements produced per this specification in accordance with their designated colors

identified per QPL-18240.

3.6 Workmanship. Workmanship shall be consistent with high-grade commercial practice.

Parts are required to be free of burrs and slivers except slight burrs are permissible in the area of

the self-locking element provided maximum locking torque values specified in table II are not

exceeded.

4. VERIFICATION

4.1 Classification of inspections. The inspection requirements specified herein are classified

as follows:

a. Qualification inspection (see 4.2).

b. Quality conformance inspection (see 4.3).

4.1.1 Responsibility of the self-locking element supplier. The self-locking element supplier

shall be responsible for compliance with all the requirements of sections 3 and 4. The seller of the

completed fastener shall be responsible for proving that the fastener product has met all the

quality conformance inspections of the completed fastener.

4.2 Qualification inspection. Qualification inspection shall be performed at a laboratory

acceptable to the Government on sample units produced with equipment and procedures normally

used in production. Qualification inspections shall be as specified in table VII. Qualification

inspection shall be limited to the fasteners shown in tables IV and shall be authorized only upon

presentation of certified test reports to the activity responsible for qualification. The test reports

shall include actual results of all the tests and a drawing which shows the location, size, material,

method of attachment and protrusion of the self-locking element for each diameter upon which

qualification is desired. A manufacturer's designation shall be submitted for the locking element

to be used in each diameter of fastener. For qualification of sizes up to and including .500"

(government designation 80), the manufacturer must submit samples for full testing to be

conducted by the qualifying test facility for each individual desired size. For qualification of sizes

above .500" nominal diameter size, the manufacturer must submit actual torque test data and

samples of the specific size to the qualifying testing facility and must be qualified to the .500"

nominal diameter size.

4.2.1 Retention of qualification. Certification shall be requested by Naval Air Warfare

Center from each manufacturer and forwarded to the preparing activity for those specifications

which do not contain a requirement for retention of qualification by testing. Certification shall be

at the time of the two year review and shall be signed by a responsible official or management,

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MIL-DTL-18240F

attesting that the listed product(s) is still available from the listed plant, and is produced under the

same conditions as originally qualified; i.e., same process, materials, construction, design,

manufacturer's part number, or designation, and meets the requirements of the current issue of the

specification. Failure to provide the certification will be cause for removal from the QPL.

4.2.2 Sampling instructions. The qualification inspection samples shall consist of 60

fasteners with the self-locking elements conforming to table IV for each diameter for which

qualification is desired. All test nuts necessary for the inspections shall conform to tables VA and

VB and shall be furnished by the manufacturer. Samples shall be identified as required and

forwarded to the activity designated in the letter of authorization from the activity responsible for

qualification (see 6.3).

4.3 Quality conformance inspection. Prior to installation of the self-locking element, the

quality conformance inspections of the applicable fastener specification shall be met. In addition,

after installation of the self-locking element on to the applicable fastener, the quality conformance

inspections specified in table VI shall be met. Also, the self-locking fastener shall meet any other

tests which are considered necessary by the procuring activity to determine conformance with the

requirements of this specification. Any rework of the fastener as defined by the Fastener Quality

Act shall require retesting.

4.3.1 Sampling. For the quality conformance inspections specified herein, the sample self-

locking fasteners shall be selected at random from each finished lot as specified in 4.3.1.1. Group

A quality conformance inspection sampling shall be in accordance with ANSI/ASQZ 1.4-1993,

single sampling inspection, Level II, of zero acceptance level. Group B torque inspection sampling

shall be in accordance with the sampling plan in table IX orX at the supplier’s option.

4.3.1.1 Lot. A lot shall consist of finished fasteners with the self-locking element

incorporated which are of the same diameter and length, fabricated by the same process, heat

treated in the same manner, and produced as one continuous run or order or part thereof,

whichever is of the smaller quantity.

4.4 Methods of inspection.

4.4.1 Examination of product. The self-locking fastener shall be examined for the following

items before any other tests are conducted..

a. Presence of self-locking element.

b. Location of self-locking element.

c. Dimensions of self-locking element.

d. Presence of burrs and slivers (see 3.6).

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MIL-DTL-18240F

e. Identification of product.

4.4.2 Torque test. For qualification testing 10 sample fasteners with self-locking elements

installed as specified in table IV shall be tested with the test nuts specified in tables VA and VB.

For quality conformance purposes, the bolts shall be as specified in the applicable document which

requires a self-locking element per MIL-DTL-18240 and the test nut shall be as specified in table

VA and VB for the correct thread type. The following test shall be performed:

NOTE: Parts that can not be seated shall be tested unseated.

a. Prior to the actual testing of self-locking screws and bolts, a test nut as

specified in table VA and table VB with the same thread form, class and pitch,

shall be gauged with a go and no go threaded plug gage. The test nut shall not

accept the no go gage for more than 1.5 turns and shall freely accept the go gage

for the entire length of the nut. The minor thread diameter shall also be checked

for conformance with table VA and VB.

b. A light lubricating oil shall be applied directly to the locking element prior to

torque testing, unless otherwise specified. ( see 6.4.1)

c. The torque shall be measured using a calibrated torque wrench in accordance

with GGG-W-686 or a digital torque sensor capable of measuring the torque

values encountered during the test. (see 6.4.2)

d. A self-locking fastener shall be assembled with hardened spacers, or washers as

necessary, and a test nut. The total thickness of the spacers and washers for the

test assembly shall be selected so that the locking element of the self-locking

fastener is fully engaged in the test nut. Set screws shall be tested in a blind hole.

If the self-locking fastener is turned, the restraining mechanism shall be such that it

imparts no radial load to the nut. For testing of self-locking fastener without

sufficient thread length for a locking element in accordance with table I or for

thread sizes not covered in table II only a positive indication of off prevailing

torque is required for five cycles. Sufficient thread length is eight threads (one

complete thread pitch, plus five complete thread pitches for the locking element,

plus two run-out pitches for ease of starting, for a total of eight threads minimum.)

Sufficient thread length may be calculated as follows:

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MIL-DTL-18240F

Sufficient Thread Length =

Where P = Thread Pitch

EXAMPLE: .250-28 Thread

Sufficient Thread Length =

1

X8=.286in

28

1

X8

P

e. First cycle test: During the first tightening of the assembly, the 1st cycle ON

PREVAILING TORQUE (see 6.5) shall be measured and recorded.. Tightening

shall be continued until the required SEATING TORQUE (see 6.5) as specified in

table II for the applicable thread size and pitch is developed. The axial clamp load

shall be reduced to zero by backing the self-locking fastener or test nut off, until

the spacers are free to rotate. Following the removal of the axial clamp load, the

1st cycle OFF PREVAILING TORQUE (see 6.5) shall be measured during the

next 360 degrees of rotation and recorded. The self-locking fastener and test nut

shall be disassembled until the locking element is disengaged. The driving speed

shall not exceed 30 RPM.

f. Second through fifth cycle tests: The self-locking fastener and test nut shall be

reassembled, seated, and disassembled four more times following the same

procedure as the 1st cycle test. The ON and OFF PREVAILING TORQUE shall

be measured and recorded for each cycle. Sufficient time shall elapse between

torquing cycles to prevent overheating of the test assembly. During the torque test

the temperature shall not be grater than 75°F above the starting temperature.

g. For qualification testing any torque value determined to be in excess of the

limitations of table II constitutes failure of this test. For quality conformance

testing determine whether the lot passes or fails in accordance with table IX

or table X.

4.4.3 High temperature torque.

a. Assemble ten new fasteners as tested in 4.4.2, steps a through d and the on cycle of

step e.

b. Bake the assemblies to 250°F ±10° for 3 hours.

c. Air cool the assemblies to room temperature for a minimum of 1 hour.

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MIL-DTL-18240F

d. Test the torque values as indicated in 4.4.2, steps e through f, starting with the first

OFF PREVAILING TORQUE. Any torque determined in this test to be in excess

of 150 percent of the maximum prevailing torque values in table II or not meeting

the minimum prevailing torque in table II constitutes failure of this test.

4.4.4 OFF PREVAILING TORQUE at maximum temperature.

a. Assemble the same ten fasteners used in paragraph 4.4.3.

b. Bake the assemblies for one hour to 250°F ±10°.

c. While the fastener is still at 250°F, determine that the OFF PREVAILING TORQUE

value shall not be less than the minimum prevailing torque value listed in table II.

4.4.5 Vibration. Sample nuts and bolts of the size and quantities specified in table III shall

be subjected to the vibration test specified in MIL-STD-1312-7, Vibration. The sample nuts and

bolts shall be assembled to the specified torque in table III and disassembled 4 times, then

reassembled and tested. The fastener assembly shall traverse the entire length of the slots in the

test fixture during the test.

4.4.5.1 Vibration failure conditions. The self-locking element shall have failed the vibration

test for any of the following conditions:

a. When any structural failure occurs in the fastener in the region of the self-locking

element during the vibration test such as a crack intersecting the region of the

threads containing the self-locking element.

b. When any nut rotates greater than 360° during 30,000 cycles.

c. When any nut can be turned completely on or off the bolt or screw, with the fingers,

during or after completion of 30,000 cycles.

4.4.6 Reusability. At the conclusion of the tests specified in 4.4.2 (and 4.4.3 and 4.4.4 for

qualification testing), the test nuts and self-locking fasteners used in this test shall be examined for

damage to the threads. Noticeable distortion or scratches deep enough to reduce the efficiency of

the threads shall be considered a failure of the self-locking element. The threads shall remain in

serviceable condition and permit the installation of a new self-locking fastener or test nut (as

applicable) freely with the fingers up to the self-locking element.

4.4.7 Noncompliance. If a sample fails to pass Group B inspection of table VI, the

manufacturer shall notify the qualifying activity and the cognizant inspection activity of such

failure and take corrective action on the materials or processes, or both, as warranted, and on all

units of products which can be corrected and which are manufactured under essentially the same

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MIL-DTL-18240F

materials and processes, and which are considered subject to the same failure. Acceptance and

shipment of the product shall be discontinued until corrective action, acceptable to the inspection

activity has been taken. After corrective action has been taken, Group B inspection shall be

repeated on additional sample units (all tests and examinations, or the test which the original

sample failed, at the option of the qualifying activity). Groups A and B inspections may be

reinstituted; however, final acceptance and shipment shall be withheld until the Group B

inspection has shown that the corrective action was successful. In the event of failure after

reinspection, information concerning the failure shall be furnished to the cognizant inspection

activity and the qualifying activity.

5. PACKAGING

5.1 Packaging. For acquisition purposes, the packaging requirements shall be as specified in

the contract or order (see 6.2). When actual packaging of material is to be performed by DoD

personnel, these personnel need to contact the responsible packaging activity to ascertain requisite

packaging requirements. Packaging requirements are maintained by the Inventory Control Point’s

packaging activity within the Military Department or Defense Agency, or within the Military

Department’s System Command. Packaging data retrieval is available from the managing Military

Department’s or Defense Agency’s automated packaging files, CD-ROM products or by

contacting the responsible packaging activity.

6. NOTES.

(This section contains information of a general or explanatory nature that may be helpful,

but is not mandatory).

6.1 Intended use. The self-locking elements covered by this specification are intended to be

incorporated in external screw threads to be used in applications where maximum temperature

does not exceed 250°F. When these self-locking elements are incorporated in external threads

and are used in compliance with MS15981, all the configurations of figure 1 are interchangeable

Type N element, plug/pellet configuration is intended to be installed via a hole drilled into the

fastener. Type L element, strip configuration is intended to be installed via a strip cut through the

threads parallel to the length of the fastener. Type P element, patch configuration is intended to

be installed without removal of any material of the fastener.A specific type should be specified

only when required by design or application requirements. The prevailing-torque values given in

this specification are conformance requirements for self-locking elements and apply only to the

combination of test conditions described in the locking torque test procedure. If the conditions of

the actual service application differs from those of 4.4.2 (e.g. internally threaded hole in a

different material, length of thread engagement, class of internal thread tolerance, speed of

driving, different plating or coating on screw or mating part) the prevailing-torque values may

vary. Such values can only be determined through testing the locking element in its application.

The plug/pellet is not recommended for sizes below .190.

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MIL-DTL-18240F

6.1.1 Cross reference.

From Configurations listed in Revision D dated 25 February 1972

Configuration A plug /pellet type superceeded by Type N

Configuration B strip type superceeded by Type L

Configuration B patch type superceeded by Type P

6.2. Acquisition requirements. Acquisition documents must specify the following:

a. Title, number, and date of this specification.

b. Issue of DODISS to be cited in the solicitation.

c. Type (see 1.2, table I and figure 1).

d. Part number in accordance with the applicable standard.

e. Packaging requirements (see 5.1).

6.3 Qualification. With respect to products requiring qualification, awards will be made only

for products which are, at the time of award of contract, qualified for inclusion in qualified

products list QPL-18240, whether or not such products have actually been so listed by that date.

The attention of the contractors is called to these requirements, and manufacturers are urged to

arrange to have the products that they propose to offer to the Federal Government tested for

qualification in order that they may be eligible to be awarded contracts or purchase orders for the

products covered by this specification. Information pertaining to qualification of products may be

obtained from the Naval Air Warfare Center Air Craft Division, Code 435200A, Bldg 2187,

48110 Shaw Rd., Unit 5, Patuxent River MD, 20670-1906.

6.3.1 Qualification evaluation. Qualification inspection and evaluation of type N (see figure

1) locking element designs were based on the protrusion of the element being in accordance with

figure 1, dimension "B". Type N designs with protrusion of "B + 0.007 inch and design that are

otherwise the same as listed, also have qualification approval. To identify the element design with

greater protrusion of the dimension "B + 0.007 inch, figure 1 of this specification, the additional

+0.007 inch protrusion must be specified on the standard or drawing for the part, for nonstandard

parts that require a specific configuration, add a "P" to the government designation.

6.4 Torque test notes

6.4.1 A light oil such as Rainkote 400 or equivalent is used in the test (4.4.2) of fasteners to

reduce wear, prevent galling or seizure, prevent fretting, and aid in the installation and removal of

fasteners. A minimum amount may be used. This will give more consistent torque test results.

6.4.2 Some torque measuring devices, such as beam wrenches, could be 20-40% off on the

lower 20 percent of the scale and should not be used.

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MIL-DTL-18240F

6.5 Definitions.

6.5.1 Self-locking externally or internally threaded fastener(s). In this specification a

"self-locking externally threaded fastener" refers to bolts, or screws, that incorporate self-locking

elements conforming to this specification.

6.5.2 ON PREVAILING TORQUE. The maximum torque occurring while the fastener is

being installed and prior to development of any axial clamp load.

6.5.3 SEATING TORQUE. The torque required to overcome the self-locking feature and

produce an axial clamp load to the test assembly.

6.5.4 OFF PREVAILING TORQUE. The maximum torque occurring while the fastener is

in motion during the first 360 degrees of rotation in the untighting direction after the test assembly

has been unseated.

6.6 Subject term (keyword) listing.

.

Plug/Pellet

Strip

Patch

6.7 Changes from previous issue. Marginal notations are not used in this revision to identify

changes with respect to the previous issue due to the extent of the changes.

6.8 Previously manufactured product. Product manufactured prior to the date of this

specification may be used until the supply is exhausted.

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MIL-DTL-18240F

TABLE I Self-locking element dimensions. (see figure 1)

Gov’t

Des.

04

Nom

dia

.112

Type ABCD

Min

.025

.053

.030

.066

.030

.084

.030

.084

.025

.089

.025

.130

.035

.146

.035

.146

.035

.146

.055

.175

.055

.175

.055

.209

.055

.209

.055

.209

.055

.240

.055

.240

MaxMinMaxMinMaxMin

L,P.250.125.115.105.312.180

.106.053.161.121

N 1/

06.138L,P.312.156.141.131.390.234

.106.066.184.144

N 1/

08.164L,P.312.156.167.157.390.234

.124.084.192.152

N1/

10.190L,P.312.156.193.183.390.234

N.124.084.208.150

40.250L,P.326.178.253.243.415.267

N.144.089.231.191

50.312L,P.364.208.315.305.468.312

N.188.130.278.222

60.375L,P.474.208.378.368.578.312

N.166.146.284.230

70.437L,P.456.250.440.430.581.375

N.166.146.301.261

80.500 2/L,P.581.250.503.493.706.375

N.166.146.301.261

90.562 2/L,P.827.278.566.552.954.417

N.199.175.363.323

100.625 2/L,P.850.278.628.616.986.417

N.197.175.363.323

120.750 2/L,P.999.312.753.7411.150.469

N.235.209.411.321

140.875 2/L,P1.143.357.878.8641.311.536

N.235.209.427.387

1601.000 2/L,P1.250.4711.003.9871.437.625

N.235.209.427.387

1801.125 2/L,P1.417.4171.1281.1121.632.625

N.266.240.516.387

2001.250 2/L,P1.604.4171.2531.2371.819.625

N.266.240.516.452

1/ Plug/Pellet is not recommended for sizes below .190.

2/ Screws .500 inch and larger may have two self-locking elements. They shall not be more than

120 degrees of thread diameter apart.

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MIL-DTL-18240F

Table IA Screw and bolt slot and hole depths for self-locking strips and pellets.

NOM

DIA

.112

.138

.164

.190

.250

.312

.375

.437

.500

.562

.625

.750

.875

1.000

1.125

1.250

SLOT

DEPTH MAX

.048

.052

.060

.062

.070

.075

.100

.100

.100

.100

.100

.100

.100

.100

.125

.125

PELLET

DEPTH MAX

.065

.080

.090

.100

.125

.125

.125

.150

.175

.175

.225

.225

.225

.250

.250

.250

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MIL-DTL-18240F

TABLE II Torque. 1/ 3/

PREVAILING

TORQUE MAX.

ON OR OFF

inch-pound

PREVAILING

TORQUE MIN.

ON OR OFF

inch-pound

SEATING

TORQUE

inch-pound ±10%

2/

.1128.05.0.5

.13815.08.01.0

.16428.012.01.5

.19045.018.02.0

.250110.040.03.0

.312190.085.05.0

.375345.0110.09.0

.437545.0150.012.0

.500850.0220.016.0

.5621,050.0270.022.0

.6251,450.0350.030.0

.7502,560.0460.045.0

.8754,180.0700.065.0

1.0006,230.0900.085.0

1.1257,800.01050.0110.0

1.25011,200.01150.0140.0

1/ These values apply to MIL-S-8879, MIL-S-7742, ASME B1.1, and FED-STD-H28/2

threads. They do not apply to Class 1A threads.

2/ These values are for testing only, and are NOT recommended installation torque values.

3/ Values for coarse and fine threads are the same.

Bolt, or screw

thread size

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MIL-DTL-18240F

TABLE III. Vibration requirements.

MIL-STD-1312/7 Vibration

Nut sizeBolt size

Bolts and nuts required

(min. of each)

.190-32

.250-28

.312-24

.375-24

.437-20

.500-20

AN3-15A

AN4-16A

AN5-16A

AN6-17A

AN7-17A

AN8-20A

5

5

5

5

5

5

Seating

Torque (in.-lb)

36

60

120

160

200

300

TABLE IV. Length and diameter of self-locking fasteners required

for qualification inspection.

Basic part no.

NAS600

NAS601

NAS602

AN3

AN4

AN5

AN6

AN7

Length dash no.

12P

12P

12P

15

16

16

17

17

Basic part no.

AN8

AN9

AN10

AN12

AN14

AN17

AN18

AN20

Length dash no.

20

21

21

21

23

24

25

27

16

MIL-DTL-18240F

TABLE VA. Dimensions of nuts required for qualification and conformance tests (inches) 1/ 2/ 3/ 4/ 5/

UNF, UNJF, UNC, UNJC THREAD FORMS

Thread sizeMinimum width

across flats

.240

.240

.302

.302

.334

.334

.365

.365

.427

.427

.490

.490

.552

.552

.678

.678

.112-48

.112-40

.138-40

.138-32

.164-36

.164-32

.190-32

.190-24

.250-28

.250-20

.312-24

.312-18

.375-24

.375-16

.437-20

.437-14

Nut

thickness

+/-.010

.165

.200

.200

.250

.250

.250

.250

.335

.285

.400

.335

.445

.335

.500

.400

.570

90-degree

csink dia

+/-.010

.132

.132

.168

.168

.194

.194

.220

.220

.281

.281

.344

.344

.406

.406

.468

.468

Minor Dia.

Min Max

.0929.0957

.0894.0922

.1148.1176

.1094.1122

.1379.1407

.1348.1377

.1605.1633

.1511.1539

.2157.2185

.2026.2054

.2722.2751

.2593.2621

.3344.3372

.3148.3176

.3888.3916

.3685.3713

Notes: 1/ Material: 300 series stainless steel.

2/ The nut minor diameter finish shall be 63 MI or better.

3/ Nut thread dimensions not listed in table VA shall conform to MIL-S-8879 for class 3B threads Threads

shall be cut not formed.

4/ For thread sizes above .437 diameter see table VB.

5/ Test nuts manufactured to MIL-F-18240 Revision E may be used until 1 year from the date of

this specification. The test nuts specified in Revision E must be used in accordance with the

requirements of Revision E.

17

MIL-DTL-18240F

TABLE VB. Dimensions of nuts required for qualification and conformance tests (inches) 1/ 2/ 3/ 4/ 5/

Thread sizeMinimum

width

across flats

.740

.740

.865

.865

.927

.927

1.052

1.052

1.240

1.240

1.427

1.427

1.615

1.812

Nut

thickness

+/-.010

.400

.615

.445

.665

.445

.727

.625

.800

.655

.890

.750

1.000

.812

.875

90-degree

csink dia

+/-.010

.531

.531

.593

.593

.656

.656

.781

.781

.906

.906

1.031

1.031

1.156

1.281

Thread

Form

Minor Dia

Min Max

.500-20

.500-13

.562-18

.562-12

.625-18

.625-11

.750-16

.750-10

.875-14

.875-9

1-12

1-8

1.125-12

1.250-12

UNF

UNJF

UNC

UNJC

UNF

UNJF

UNC

UNJC

UNF

UNJF

UNC

UNJC

UNF

UNJF

UNC

UNJC

UNF

UNJF

UNC

UNJC

UNF

UNJF

UNC

UNJC

UNF

UNJF

UNF

UNJF

.4484

.4537

.4212

.4295

.5048

.5110

.4767

.4849

.5675

.5734

.5316

.5405

.6844

.6915

.6463

.6566

.8004

.8084

.7596

.7715

.9124

.9219

.8699

.8833

1.0374

1.0464

1.1624

1.1714

.4514

.4567

.4242

.4325

.5078

.5140

.4797

.4879

.5705

.5764

.5346

.5434

.6884

.6955

.6503

.6606

.8044

.8124

.7636

.7755

.9174

.9269

.8749

.8883

1.0424

1.0514

1.1674

1.1764

Notes: 1/ Material: 300 series stainless steel.

2/ The nut minor diameter finish shall be 63 MI or better.

3/ Nut thread dimensions not listed in table VB shall conform to MIL-S-8879 for class 3Bthreads. Threads

shall be cut not formed.

4/ For thread sizes less than .500 diameter see table VA.

6/Test nuts manufactured to MIL-F-18240 Revision E may be used until 1 year from the date of this

specification. The test nuts specified in Revision E must be used in accordance with the

requirements of Revision E

18

MIL-DTL-18240F

TABLE VI. Quality conformance inspection.

Examination or test

Group A

Examination of product:

Presence of self-locking element

Location of self-locking element

Dimensions of self-locking element

Presence of burrs and slivers

Identification of product

Group B

Torque

Reusability

Requirement

Paragraph

3.2

3.2.1

3.2.1

3.6

3.5

3.3.1

3.4

Test

Paragraph

4.4.1

4.4.1a

4.4.1b

4.4.1c

4.4.1d

4.4.1e

4.4.2

4.4.6

TABLE VII. Qualification tests.

Requirement

paragraph

Test method

paragraphInspection

Torque

High temperature torque

Off prevailing torque at

maximum temperature

Vibration

Identification of product

Examination of product

Reusability

3.3.1

3.3.2

3.3.3

3.3.4

3.5

3.2 & 3.6

3.4

4.4.2

4.4.3

4.4.4

4.4.5

4.4.1

4.4.1

4.4.6

19

MIL-DTL-18240F

TABLE VIII. Basic color limits for self-locking element.

BASIC COLORLIMITS

Per ASTM D1535

10.0B min., 8 Chroma min., 6 value min.

7.5PB max., 10 Chroma min., 4 value min.

2.5PB min., 10 Chroma min., 4 value min.

10.0G max., 4 Chroma min., 4 value min.

7.5 G 4 Chroma min., 4 value min.

5.0 G min., 4 Chroma min., 4 value min.

5.0RP min., 8 Chroma min., 5 value max.

7.5RP 8 Chroma min., 5 value max.

10.0RP max., 8 Chroma min., 5 value max.

10.0Y max., 2 Chroma min., 6 value min.

7.5 Y 2 Chroma min., 6 value min.

5.0 Y min., 2 Chroma min., 6 value min.

10.0R max., 8 Chroma min., 5 value min.

7.5 R 8 Chroma min., 5 value min.

5.0 R min., 8 Chroma min., 5 value min.

N 9.5 max. / 90.0 % R

N / 46.8 % R

Blue

Green

Plum

Yellow

Red

White

2.5YR min., 4 Chroma min., 4 value max.

5.0YR 4 Chroma min., 4 value max.

7.5YR max., 4 Chroma min., 4 value max.

(See QPL-18240 for current approved sources)

Brown

20

MIL-DTL-18240F

Table IX Variables sampling for self-locking screw torque 1/ 2/.

LOT SIZESAMPLE

NUMBER

FIRST

SECOND

FIRST

SECOND

FIRST

SECOND

FIRST

SECOND

FIRST

SECOND

FIRST

SECOND

SAMPLE

SIZE

4

8

5

10

6

12

7

14

8

16

10

20

TOTALFIRST

SAMPLE

K

A

2.42

2.21

2.22

2.32

2.48

FIRST

SAMPLE

K

R

1.35

.89

.94

1.10

.99

COMBINED

SAMPLES K

T

1.72

1.74

1.70

1.78

1.81

UNDER

151

151 THRU

300

301 THRU

500

501 THRU

1300

1301

THRU

3200

OVER

3200

1/

4

12

5

15

6

18

7

21

8

24

10

30

2.341.311.80

Evaluate each sample for on prevailing torque on the first cycle as follows:

First sample: Accept if

X

MAX1

+K

A

S

MAX1

≤M

. Reject if

X

MAX1

+K

R

S

MAX1

>M

.

Take second sample if lot is not accepted or rejected.

Second Sample: Accept if

X

MAXT

+K

T

S

MAXT

≤M

. Reject if

X

MAXT

+K

T

S

MAXT

>M

.

Evaluate each sample for off prevailing torque on the fifth cycle as follows:

First sample: Accept if

X

MIN1

−K

A

S

MIN1

≥L

. Reject if

X

MIN1

−K

R

S

MIN1

.

Take second sample if lot is not accepted or rejected.

Second Sample: Accept if

X

MINT

-

K

T

S

MINT

≥L

. Reject if

X

MINT

−K

T

S

MINT

.

2/

Definition of terms:

M

L

X

MAX1

X

MAX1

X

MIN1

= Maximum on prevailing torque specification limit per table II

= Minimum off prevailing torque specification limit per table II

= Individual on prevailing torque values on the 1st cycle

= Average of X

MAX1

values

= Individual off prevailing torque values on the 5th cycle

= Average of X

MIN1

values

x

MIN1

21

MIL-DTL-18240F

X

MAXT

= Individual on prevailing torque values on the 1st cycle for combined samples

X

MAXT

= Average of

X

MAXT

values

X

MINT

= Individual off prevailing torque values on the 5th cycle for combined samples

x

MINT

N

1

N

T

S

S

S

S

= Average of

X

MINT

values

= Number of parts in first sample

= Number of parts in combined sample

N

N

N

N

MAX1

=

=

=

=

1

∑

T

X

2

MAX1

−(

∑

X

1

MAX1

)

2

)

2

N

1

(N−1)

MAXT

MAXT

∑

X

X

2

MAXT

−(

∑

X

T

N

1

T

(N−1)

MIN1

MIN1

∑

T

−(

∑

X

N

1

(N

1

−1)

2

MIN1

2

MINT

)

2

)

2

MINT

∑

X−(

∑

X

T

MINT

N

T

(N−1)

TABLE X Attribute plan for quality conformance torque tests.

Lot size

Under 10,000

10,000 through 50,000

50,001 through 100,000

Over 100,000

Sample Size

10

15

20

32

Acceptance number of failed parts

0

0

0

0

22

MIL-DTL-18240F

TYPE PTYPE NTYPE L

Figure 1. 250 degree F Self-locking elements for externally threaded fasteners.

CONCLUDING MATERIAL

Custodians:

Navy - AS

Air Force - 11

Army - AV

Review activities:

Navy - OS

Air Force - 99

Army - AR, EA, MI

DLA - IS

Preparing activity:

Navy - AS

(Project 53GP-0283)

23

STANDARDIZATION DOCUMENT IMPROVEMENT PROPOSAL

1.

2.

3.

The preparing activity must complete blocks 1, 2, 3, and 8. In block 1, both the document number and revision letter should be

given.

The submitter of this form must complete blocks 4, 5, 6, and 7.

The preparing activity must provide a reply within 30 days from receipt of the form.

INSTRUCTIONS

NOTE: This form may not be used to request copies of documents, nor to request waivers, or clarification of requirements on current

contracts. Comments submitted on this form do not constitute or imply authorization to waive any portion of the referenced

document(s) or to amend contractual requirements.

MIL-DTL-18240F

970602

3. DOCUMENT TITLE

FASTENER ELEMENT, SELF-LOCKING, THREADED FASTENER, 250 DEG. F MAXIMUM

I RECOMMEND A CHANGE:

1. DOCUMENT NUMBER2. DOCUMENT DATE (YYMMDD)

5. REASON FOR RECOMMENDATION

6. SUBMITTER

a. NAME (Last, First, Middle Initial)

c. ADDRESS (Include Zip Code)

b. ORGANIZATION

d. TELEPHONE (Include Area Code)

(1) Commercial

(2) AUTOVON

(if applicable)

8. PREPARING ACTIVITY

a. NAMEb. TELEPHONE Include Area Code)

(1) Commercial

(908) 323-7488

SUBMITTED

(YYMMDD)

COMMANDER, NAVAL AIR WARFARE CENTER,

AIRCRAFT DIVISION

c. ADDRESS (Include Zip Code)

CODE 4.1.4

HIGHWAY 547

LAKEHURST, NJ 08733-5100

(2) AUTOVON

624-7488

IF YOU DO NOT RECEIVE A REPLY WITHIN 45 DAYS, CONTACT:

DEFENSE QUALITY AND STANDARDIZATION OFFICE

5203 Leesburg Pike, Suite 1403, Falls Church, VA 22401-3466

Telephone (703) 756-2340AUTOVON 289-2340

Previous editions are obsolete.198/290

DD Form 1426, OCT 89