SAE AS 8879D-2004_图文

REV.

D

AS8879

AEROSPACE

Issued 1996-10

STANDARD

Revised 2004-08

®

Superseding AS8879C

Screw Threads - UNJ Profile, Inch

Controlled Radius Root with Increased Minor Diameter

FOREWORD

This standard was generated to provide an alternative to the inactive government specification

MIL-S- 8879 for screw threads - UNJ profile, inch.

This standard has been revised to focus on the design requirements for screw threads – UNJ

profile, inch. Procurement information not directly related to the design standard, such as

product acceptance and quality assurance, have been removed.

A whitepaper has been developed to provide some history on the development of screw thread

standards (MIL-S-8879 and AS8879) and the rationale for the content of AS8879 Revision C.

This whitepaper will be published in the future by the SAE as an Aerospace Information Report

(AIR5926).

SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is

entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.”

SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.

Copyright © 2004 SAE International

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying,

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Author:Gilligan-SID:9234-GUID:30691668-155.69.4.4

SAE AS8879 Revision D

1. SCOPE:

This SAE Aerospace Standard (AS) specifies the characteristics of screw threads - UNJ

profile inch series, including a mandatory controlled radius as specified in Table 1 at the root

of the external thread. The minor diameter of both external and internal threads provides a

basic thread height of .5625H to accommodate the external thread maximum root radius.

The following detailed design requirements are included:

a. Screw threads - UNJ basic profile and design profiles.

b. Standard series of diameter-pitch combinations for nominal thread diameters from 0.060

to 6.000 inches.

c. Standard thread classes and form tolerances.

d. Formulae for thread dimensions and tolerances.

e. Method of designating UNJ threads.

f. Tables for selected diameter-pitch combinations for close tolerance mechanical thread

applications.

g. Tables for screw thread - UNJ profile thread limit dimensions.

1.1 Purpose:

This document specifies the geometric design for each characteristic of screw threads -

UNJ profile inch series and the conformance requirements. In addition, the purpose of this

standard is to:

a. Define the geometric requirements for a selected series of Unified Screw Threads,

modified to provide a radius at the external thread root.

b. Establish requirements for a continuous radius at the root of the external threads.

c. Establish requirements for an increase in the minor diameter of both internal and

external threads to accommodate the external thread root radius.

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SAE AS8879 Revision D

2. REFERENCES:

2.1 Applicable Documents:

The following publications form a part of this document to the extent specified herein. The

applicable issue of all publications shall be the issue in effect on the date of the purchase

order. In the event of conflict between the text in this document and the references cited

herein, the text in this document takes precedence. Nothing in this document, however,

supersedes applicable laws and regulations unless a specific exemption has been

obtained.

2.1.1 ASME Publications: Available from the American Society of Mechanical Engineering

(ASME) through the web at or in writing at ASME, 22 Law Drive,

Box 2900, Fairfield, NJ 07007-2900.

ASME B1.1

ASME B1.2

ASME B1.3

ASME B1.7

ASME B46.1

ASME B47.1

Unified Inch Screw Threads (UN and UNR Thread Form)

Gages and Gaging for Unified Inch Screw Threads

Screw Thread Gaging System for Dimensional Acceptability - Inch

and Metric Screw Threads (UN, UNR, UNJ, M, and MJ)

Nomenclature, Definitions, and Letter Symbols for Screw Threads

Surface Texture (Surface Roughness, Waviness and Lay)

Gage Blanks

2.1.2 Government Publications: Available from The Department of Defense Single Stock

Point for Military Specifications, Standards and Related Publications (DODSSP) through

the web at or in writing at DODSSP, Building 4 / Section D,

700 Robbins Avenue, Philadelphia, PA 19111-5098.

FED-STD-H28/6 Gages and Gaging for Unified Screw Threads – UN and UNR

Thread Forms

FED-STD-H28/20 Inspection Methods for Acceptability of UN, UNR, UNJ, M and MJ

Screw Threads

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Author:Gilligan-SID:9234-GUID:30691668-155.69.4.4

SAE AS8879 Revision D

3. DESIGN REQUIREMENTS:

Threads produced in accordance with this design standard shall be within the basic design

profile, dimensional limits and tolerances specified in Tables 1 through 7, and Table 9. (See

Figures 1, 2 and 3 for illustrations of thread characteristics.)

3.1 Thread Series:

This standard defines two series of threads, standard UNJ and special UNJ.

3.1.1 Standard UNJ Series: The standard UNJ series of threads consists of three series with

graded pitches (coarse, fine, and extra fine) and three series with constant pitches (8,

12, and 16 threads per inch). Standard UNJ threads shall be selected from those with

diameter-pitch combinations listed in Tables 2 through 7.

3.1.2 Special UNJ Series: The special UNJ series of threads consists of all controlled root

radius threads with combinations of diameter and pitch that are not included in the

standard UNJ series.

3.2 Thread Characteristics:

3.2.1 General Data:

3.2.1.1 Basic Thread Data: The basic thread data for threads with standard pitches is shown

in Table 1. This table is provided for engineering reference only.

3.2.1.2 Standard UNJ Thread Data: Thread dimensions are specified in Tables 2 through 7

for the diameter-pitch combinations shown herein. Dimensions include pitch diameter,

major diameter, minor diameter, and external thread root radius. Functional diameter

(Maximum Material) shall be within pitch diameter limits.

3.2.1.3 Special UNJ Thread Data: Dimensions for threads of special diameter-pitch

combinations shall be computed from the formulas in Table 9. Functional diameter

(Maximum Material) shall be within pitch diameter limits.

3.2.2 External threads: External threads shall be of Unified form, in accordance with ASME

B1.1 (Class 3A), altered at the root so that the flanks of the adjacent threads are joined

by one continuous smoothly blended curve tangent to the flanks. The root radius (radius

of curvature) tangent to the flanks shall be within the values given in Tables 2 through 7

(see Figures 1 and 3).

3.2.3 Internal Threads: The internal threads shall be of the Unified form, in accordance with

ASME B1.1 (Class 3B), modified at the minor diameter (truncated to 5H/16) to the

values given in Tables 2 through 7 (see Figures 2 and 3).

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SAE AS8879 Revision D

3.3 Thread Categories:

This standard defines design requirements for two thread categories. Several

characteristics, which are provided as reference-only for Category 1 threads, are design

requirements for Category 2 threads. However, the basic design profile and dimensions

specified in Tables 2 through 7 and Table 9 are the same for both thread categories.

Thread category shall be determined and specified with the thread designation on the

drawing or referenced specification for threaded product in accordance with this standard.

When a thread category is not specified, Category 1 design requirements shall apply.

3.3.1 Category 1 Threads: The design characteristics for Category 1 threads are specified in

Table 8. Several design characteristics are reference-only for Category 1 threads.

3.3.2 Category 2 Threads: The design characteristics for Category 2 threads are specified in

Table 8.

3.4 Limits of Size:

Category 1 and Category 2 threads shall be within the limits of size specified in Tables 2

through 7.

3.4.1 Variations, Category 1 Threads: Lead, flank angle, circularity (roundness), taper, and

runout are reference-only dimensions for Category 1 threads. Note: Establishing

conformance of a product thread for maximum and minimum material also establishes

that the combined effects of these variations are within limits.

3.4.2 Variations, Category 2 Threads: Lead, flank angle, circularity (roundness), taper, and

runout are design requirements for Category 2 threads. The combined effect of

variations in these characteristics are satisfactory when the difference between

functional diameter and pitch diameter is less than, or equal to, 40% of the pitch

diameter tolerance. This requirement applies only to full form threads. If the difference

between functional diameter and pitch diameter exceeds 40% pitch diameter tolerance,

then the following requirements apply individually.

3.4.2.1 Lead: The lead is the number of thread starts divided by the number of threads per

inch. The variation in the lead (including helix variation) measured over a distance not

less than the go ring gage blank (as defined in ASME B 47.1) shall not exceed a value

equivalent to 40% of the pitch diameter tolerance. Where product full form thread

length is less than the gage blank length, the product thread lead variation is

acceptable when functional diameter is within limits.

3.4.2.2 Flank Angle: The flank angle shall be 30 degrees. Flank angle variation shall not

exceed a value equivalent to 40% of the pitch diameter tolerance.

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SAE AS8879 Revision D

3.4.2.3 Circularity (Roundness): The pitch diameter shall be circular within one-half the pitch

diameter tolerance where pitch diameter tolerance is less than 0.004 inch. Where

pitch diameter tolerance is 0.004 inch or larger, the pitch diameter shall be circular

within 0.002 inch. When circularity is checked using pitch diameter indicating gage

segments or rolls, the circularity value is equal to one-half the difference between

maximum and the minimum pitch diameter readings. Threads 1.5000 inches and

larger with 16 threads per inch or less may exceed the tolerance by 0.002 inch over a

maximum arc of 15 degrees, in the direction of minimum material in this area provided

that this overcut does not result in raised material on the thread flanks or roots.

Circularity shall fall within the pitch diameter tolerance except above the 15 degree

arc.

3.4.2.4 Taper: Taper of the pitch diameter based on the length of engagement in 6.3 shall be

within 0.4 of the pitch diameter tolerance.

3.4.2.5 Runout: The circular runout of the external thread major diameter cylinder and the

internal thread minor diameter cylinder with respect to the pitch diameter cylinder shall

not exceed twice the pitch diameter tolerance.

3.5 Incomplete Threads:

3.5.1 Incomplete Runout Threads: Unless otherwise specified, threads on externally threaded

parts shall terminate between one and two pitches from the start of the unthreaded

section, end of full form thread, or fillet radius, as applicable. The root radius of the

incomplete thread shall be greater than or equal to the minimum root radius listed in

Table 1 and shall transition gradually onto the unthreaded portion. There is no upper

limit on root radius of incomplete threads as long as all other requirements are met. For

parts with internal through threads, the incomplete runout threads shall not exceed 2

incomplete pitches.

3.5.2 Incomplete Lead Threads: Unless otherwise specified, the entering end of external

threads and internal threads may be outside the specified limits of size for a length not to

exceed two pitches, including chamfer. In no case shall the lead threads exceed the

specified maximum material condition.

3.6 Surface Roughness:

On certain parts, it may be necessary to control the surface roughness of the thread

flanks, roots, or crests. This requirement shall be specified, if necessary, on the part

drawing or specification. Surface roughness specifications should be commensurate with

a realistic assessment of current production capabilities. For Category 1 and 2 threads,

unless otherwise specified, the surface roughness of the thread flanks and the roots shall

be no greater than 63 µin Ra for external threads and 100 µin Ra for internal threads in

accordance with ASME B46.1.

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SAE AS8879 Revision D

3.7 Material Limits for Coated or Plated Threads:

3.7.1 External threads: Unless otherwise specified, when externally threaded parts are to be

coated/ plated, the minimum major diameter and minimum minor diameter may be

reduced by 2 times the minimum plating or coating thickness. The minimum pitch

diameter before coating may be reduced by no more than 0.001 inch for threads with

pitch diameter tolerance not exceeding 0.0035 inch. For threads with pitch diameter

tolerance greater than 0.0035 inch, the minimum pitch diameter may be reduced by an

amount equal to 0.3 times the pitch diameter tolerance but not more than 0.0015 inch.

Unless otherwise specified, all external thread characteristics shall be within the

adjusted dimensional requirements before coating or plating. After coating or plating,

the threads shall not exceed maximum material limits.

3.7.2 Internal Threads: Unless otherwise specified, the minor diameter of internal threads to

be coated or plated may be increased by 2 times the minimum plating or coating

thickness. The maximum pitch diameter requirement may be increased by the same

values as the reductions allowed for external threads. Unless otherwise specified, all

internal thread characteristics shall be within the adjusted dimensional requirements

before coating or plating. After coating or plating, the threads shall not exceed maximum

material limits.

3.7.3 Coating threads with Solid Film Lubricant: An adjustment of pitch diameter to

accommodate the thickness of solid film lubricant is not in addition to that specified in

3.7.1 and 3.7.2. The product thread, before application of solid film lubricant, shall

comply with AS8879 dimensions.

4. DIMENSIONAL CONFORMANCE:

4.1 Dimensional Conformance:

Unless otherwise specified on drawings or product specifications, threads shall conform to

the design requirements of this standard as specified in Table 8.

4.2 Methods of Inspection:

All methods of inspecting the dimensional characteristics of thread forms presented in

FED-STD- H28/20, ASME B1.3, and new, or more effective methods are acceptable so

long as they have been demonstrated to show and assure conformance of the threads to

the requirements of this standard and drawings, product specifications, or specification

sheets supporting or derived from this standard. Gages shall meet the requirements of

FED-STD-H28/6, ASME B1.2, and FED-STD-H28/ 20; new, or more effective methods are

acceptable.

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SAE AS8879 Revision D

4.2.1 Evaluating Threads After Alteration: For configuration changes to the threads such as

self-locking features, castellations, keyways, cotter pin holes and similar features; care

must be exercised to inspect undistorted, uninterrupted, full form threads. When

maximum and minimum material conformity cannot be accomplished on a completed

screw thread product because of a configuration change to the threads (e.g.,

deformation, slots, self-locking devices), the product screw threads shall be inspected

for conformance at a point of manufacture prior to the configuration change.

5. THREAD DESIGNATION:

5.1 Thread Designation:

The threads described herein shall be designated in the following manner indicating the

nominal diameter, number of threads per inch, thread series symbol (that is, thread form,

controlled root symbol and thread series), and thread class including the external "A" or

internal "B" thread symbol. Specify design category 1 or 2 when required. Omitting a

category designation defaults to design category 1.

5.1.1 Standard UNJ Thread Designations: Threads selected from the standard UNJ series

shall be specified as shown in the following examples.

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Author:Gilligan-SID:9234-GUID:30691668-155.69.4.4

SAE AS8879 Revision D

5.1.2 Special UNJ Thread Designations: The identifying letter "S" shall be included in the

thread series symbol to indicate a special thread. Special diameter-pitch combinations

developed in accordance with this standard shall be designated as shown in the

following examples.

External Thread:

1.3125-32 UNJS-3A thread per AS8879

Major Diameter 1.3065 - 1.3125

Pitch Diameter 1.2541 - 1.2922

Minor Diameter 1.2364 - 1.2764

Root Radius .0047 - .0056

6. INFORMATION FOR GUIDANCE ONLY:

The following comments are intended to clarify subjects related to this standard and are not

to be construed as screw thread requirements.

6.1 Basic Design Profile:

The basic design profile of the threads in this document, the diameter-pitch combinations,

and tolerances are based on the Unified Inch standard. These profiles are not

interchangeable with Metric (M and MJ) or UN profile inch screw threads. The UNJ

internal thread will assemble with the UN series external thread. Mating the UNJ series

external thread with the UN series internal thread should be avoided due to a potential

interference at the minor diameter. However, since the UNJ profile and tolerances for

aerospace screw threads - UNJ profile (inch series) in international standard ISO 3161

and ASME B1.15 (Class 3) were based on MIL-S-8879, the resultant thread geometry is

interchangeable with the thread form in AS8879.

6.2 Preferred Thread Selection:

The use of standard UNJ threads should be given first consideration in the design of new

equipment. Within standard UNJ series, the use of fine threads (UNJF series) should be

used whenever practicable for 0.1900 through 1.5000 inch diameter threads (see Table 3).

For smaller diameters, the use of coarse threads (UNJC series) is recommended (see

Table 2). For larger diameters, the constant pitch 12 thread per inch series is

recommended (see Table 6).

6.3 Basis for Pitch Diameter Tolerances in Tables 2 Through 7:

The length of engagement for UNJC, UNJF, and the 8UNJ series threads upon which their

specified tolerances are based is equal to the basic major diameter. These tolerances are

applicable for the lengths of engagement of these threads up to 1.5 times the basic major

diameter. The length of engagement for UNJEF, 12UNJ, and 16UNJ series threads upon

which their specified tolerances are based is equal to 9 pitches. These tolerances are

applicable for lengths of engagement of these threads up to 15 pitches.

Internal Thread:

8.750-8 UNJS-3B thread per AS8879

Major Diameter 8.750 MIN

Pitch Diameter 8.6688 - 8.6769

Minor Diameter 8.6282 - 8.6432

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Author:Gilligan-SID:9234-GUID:30691668-155.69.4.4

SAE AS8879 Revision D

6.4 Clarification of Tools and Gages:

6.4.1 Use of Unified Thread Tools and Gages: The following UN form tools and gages may be

used for UNJ threads covered by this standard:

a. Taps and thread gages for Class 3B. Minor diameter gages must meet the

requirements of this standard.

b. Thread gages for Class 3A, except crest truncation of the maximum material thread

gage must be increased to 0.3125p flat.

6.5 ASME Gaging Systems:

The ASME B1 Committee has established systems of gaging that support evaluation of

product thread geometry. See ASME B1.3.

6.5.1 System 22 Definition: System 22 is a group or set of gages that permit evaluation of

functional size at the maximum material limits within the length of the standard gaging

elements, and also permits evaluation of the minimum-material size limits over the

length of the full thread. The cumulative variation of thread form deviations such as

lead, flank angle, taper, and roundness is contained within the maximum- and minimum-material limits. Gaging elements for determining individual feature form deviations is not

included in System 22.

6.5.2 System 23 Definition: System 23 is a group or set of gages that permit evaluation of

functional size at the maximum-material limits within the length of the standard gaging

elements, and also permits evaluation of the minimum-material size limits over the

length of the full thread. The System 23 group or set of gages includes those necessary

for evaluation of thread form deviations such as lead, flank angle, taper, and roundness.

6.6 Definitions:

Terms for thread characteristics, nomenclature, definitions, and letter symbols are

provided in ASME B1.7.

6.7 The change bar ( l ) located in the left margin is for the convenience of the user in locating

areas where technical revisions, not editorial changes, have been made to the previous

issue of this document. An (R) symbol to the left of the document title indicates a

complete revision of the document.

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SAE AS8879 Revision D

TABLE 1 - Basic Thread Data

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SAE AS8879 Revision D

TABLE 1 - Basic Thread Data (Continued)

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SAE AS8879 Revision D

TABLE 2 - Coarse Thread Series

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SAE AS8879 Revision D

TABLE 3 - Fine Thread Series

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SAE AS8879 Revision D

TABLE 4 - Extra Fine Thread Series

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SAE AS8879 Revision D

TABLE 5 - Eight Thread Series

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SAE AS8879 Revision D

TABLE 6 - Twelve Thread Series

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SAE AS8879 Revision D

TABLE 6 - Twelve Thread Series (Continued)

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SAE AS8879 Revision D

TABLE 7 - Sixteen Thread Series

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SAE AS8879 Revision D

TABLE 7 - Sixteen Thread Series (Continued)

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SAE AS8879 Revision D

TABLE 8 - Dimensional Design and Conformance Requirements

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SAE AS8879 Revision D

TABLE 9 - Special Diameter-Pitch Combinations

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SAE AS8879 Revision D

FIGURE 1 - External Thread Maximum Material Condition

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SAE AS8879 Revision D

FIGURE 2 - Internal Thread Maximum Material Condition

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SAE AS8879 Revision D

FIGURE 3 - Disposition of Tolerances and Crest Clearances

PREPARED UNDER THE JURISDICTION OF

THE AEROSPACE INDUSTRY SCREW THREAD CONFORMITY

TASK FORCE (STC-TF) AND SAE COMMITTEE E-25, GENERAL STANDARDS FOR

AEROSPACE AND PROPULSION SYSTEMS

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