1、I AN ASME STANDARD Unified Inch Screw Threads (UNJ Thread Form) The American Society of I I Mechanical Engineers L I I 345 East 47th Street, New York, N.Y. - Date of Issuance: August 15, 1995 This Standard will be revised when the Society approves the issuance of a new edition. There will be no adde
2、nda or written interpretations of the requirements of this Standard issued to this Edition. ASME is the registered trademark of The American Society of Mechanical Engineers. This code or standard was developed under procedures accredited as meeting the criteria for American National Standards. The C
3、onsensus Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an opportunity to participate. The proposed code or standard was made available for public review and comment which provides an opportunity for additional pub
4、lic input from industry, academia, regulatory agen- cies, and the public-at-large. ASME does not “approve,“ “rate,“ or “endorse“ any item, construction, proprietary device, or activity. ASME does not take any position with respect to the validity of any patent rights asserted in connection with any
5、items mentioned in this document, and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable Letters Patent, nor assume any such liability. Users of a code or standard are expressly advised that determination of the validity of any such patent r
6、ights, and the risk of infringement of such rights, isentirely their own responsibility. Participation by federal agency representative(s) or person(s) affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard. ASME accepts responsibility for on
7、ly those interpretations issued in accordance with governing ASME procedures and policies which preclude the issuance of interpretations by individual volun- teers. No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permi
8、ssion of the publisher. Copyright O 1995 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Resewed Printed in U.S.A. FOREWORD (This Foreword is not part of ASME 81.15-1995.) This Standard is similar to Military Specification MIL-S-8879 and equivalent to ISO- 3161-1977 for thread Classes 3A
9、and 3B. British Standard BS 4084: 1978 including Amend- ment 1 is technically identical to ISO-3161-1977 except for Appendix A which provides information for a 20 UNJ constant pitch series for diameters through 3 inches. The UNJ thread form, having the enlarged root radius in the external thread, wa
10、s introduced for applications requiring high fatigue strength where working stress levels are high, in order to minimize size and weight in parts, as in aerospace applications and also for other designs in commercial products where stresses are critical. To meet these requirements, the UNJ external
11、thread root radius is designed between 0.1501 1Pto 0.18042P and the minor diameter of the mating internal thread is increased to ensure the necessary clearance. This Standard includes Classes 2A and 2B UNJ screw threads. Either Class 3 or Class 2 UNJ threads are appropriate for commercial applicatio
12、ns commensurate with the fatigue and stress levels required. It is not recommended that Classes 2A and 2B threads be used for aerospace applications. Only UNJ thread Classes 3A and 3B meet the requirements of Military Specification MIL- S-8879. NOTE: In what follows, the symbols Hand h are used. His
13、 defined as the height of the sharp vee thread formed by extending the thread flanks until they meet. H is equal to.0.866025 times the pitch, P. The symbol h is equal to 0.75 times H and represents the theoretical height of the American National thread form. It is still used as the basis for the val
14、ue called percent of thread. The UNJ thread form is the UN thread form modified to 9/1a H or 75% h basic thread depth which allows the 0.18042P maximum root radius in the external thread. The first known U.S. standard of similar thread form was the Society of Automotive Engineers Aeronautical Standa
15、rd AS 82 published in March 1942, which is a modified American National thread form to 75% h basic thread depth and specifying 0.108P-0.180P root radius in the external thread. This thread was symbolized NR, National Round, and was developed for aircraft engine applications. Tension-tension fatigue
16、testing of aircraft fasteners in 1942 demonstrated the importance of the external thread root contour in the fatigue life of a screw thread rolled after heat treatment. Fatigue testing isolated the following elements of good external thread root design: The root should be radiused, not sharp. Theore
17、tically, it should be a continuous circular arc, blending smoothly with the thread flanks. The radius should be as large as possible within the allowable design form. The root contour should be smooth throughout, free of any imperfections, tool marks, or other minor notches. Recognizing the need for
18、 improved 160,000 psi tensile strength bolts, the Military Services published in April 1952, MIL-B-7838A bolt procurement specification for aircraft applications based on the Unified thread form having 83/3% h Unified thread form. Thus, larger external root radius requires a shallower internal threa
19、d depth to clear the flank tangency point. Although the Unified internal thread standards for tap drill sizes permit depths of more than 75,% h, production rarely used these drills because deeper tapping of internal threads is generally not considered economically practical. A few internal threads h
20、ave depths as great as 70% h, but the vast majority lie between 60% and 68% h. Since internal threads are generally less than 75% h basic thread depth, the root radius of the external thread was increased to 0.150P min. and 0.180P max. for the 180,000 psi and higher tensile strength bolts. This exte
21、rnal thread form was developed in 1955 by the aerospace fastener industry and was known as the “Hi R“ thread form. Through the coordinated effort with the Aerospace Engine and Propeller Utility Stan- dards parts Committee E25 of SAE and the AIA National Aerospace Standards Committee NASC, the Air Fo
22、rce and Navy developed and published in September 1960, the thread specification MIL-S-8879 which features the “Hi R“ thread root radius in the external thread and the internal thread modified to 9/6 H basic or 75% h thread depth. With the advent of aircraft gas turbine engines, the high temperature
23、 threaded fasteners developed better elevated temperature performance using MIL-S-8879 UNJ thread root radius, in that the stress-rupture life of bolts was greatly improved. The UNJ thread form has been adopted by the aerospace industry as the all-purpose thread standard, with the exception of elect
24、rical hardware and thread sizes 0.138 and smaller, which may use the UN thread form. Suggestions for improvement of this Standard will be welcome. They should be sent to The American Society of Mechanical Engineers, Att: Secretary, B1 Main Committee, 345 East 47th Street, New York, NY 10017. This St
25、andard was approved as an ASME Standard on June 22, 1993. ASME STANDARDS COMMllTEE 61 Standardization and Unification of Screw Threads (The following is the roster of the Committee at the time of approval of this Standard.) OFFICERS E. Schwartz, Chairman K. E. McCullough, Vice Chairman C. J. Gornez.
26、 Secretary COMMllTEE PERSONNEL J. R. Anderson R. J. Browning R. M. Byrne D. P. Cadieux F. G. Calderone F. H. Cantrell R. S. Chamerda R. Dodge P. H. Drake A. E. Ellis H. W. Ellison C. G. Erickson W. C. Farrell, Jr. R. E. Ferry, Jr. G. A. Flannery D. S. George J. Greenslade J. 0. Heinze R. R. Hyman C.
27、 W. Jatho S. P. Johnson S. I. Kanter J. Krippes R. W. Lamport R. S. LaNier J. B. Levy J. C. McMurray D. Miskinis W. R. Newman A. Painter G. A. Russ R. J. Sabatos D. M. Satava M. M. Schuster R. H. Searr R. E. Seppey A. D. Shepherd, Jr. V. B. Shook A. G. Strang J. F. Sullivan R. L. Tennis A. F. Thibod
28、eau A. M. Wilkerson C. J. Wilson SUBCOMMllTEE B1.15-UNJ SCREW THREADS R. E. Seppey, Chairman F. H. Cantrell R. S. Chamerda L. N. Dixon, Jr. R. E. Ferry, Jr. G. A. Flannery D. S. George S. I. Kanter J. Krippes K. E. McCullough W. R. Newman A. Painter G. A. Russ M. M. Schuster A. G. Strang R. L. Tenni
29、s A. M. Wilkerson C. J. Wilson CONTENTS . Foreword 111 . Standards Committee Roster v 1 General 1.1 Scope 1.2 Field of Application . . 1.3 Assembly 1.4 Federal Government Use . 1.5 References 2 Profile of Thread . 2.1 Basic Profile . 2.2 Basic Thread Profile Symbols 2.3 Design Profiles 2.4 Root Radi
30、us of the Thread 3 Series of Threads 4 Thread Characteristics . 4.1 Length of Thread Engagement. LE . 4.2 Tolerance System . 4.3 Limits of Size . 4.4 Thread Form Tolerances . 5 Dimensional Accommodation of Coatings and Platings 5.1 . Coated External Threads - Class 3A 5.2 Coating Threads with Dry Fi
31、lm Lubricant 5.3 Coated External Threads - Class 2A 5.4 Coated Internal Threads - Classes 2B and 3B 6 Designation of Threads 6.1 Basic Designation 6.2 Standard Thread Series Designation 6.3 Designation of Coated Threads 6.4 Designation of Threads Having Modified Crests 6.5 Designation of Threads Hav
32、ing Special Length Requirements . 6.6 Designation of Special Series Threads 7 Acceptability Figures 1 Basic Profile 4 2 Internal UNJ Thread Design Profile and Tolerances . 4 3 External UNJ Thread Design Profile and Tolerances 5 4 Root Radius of External Thread 5 Tables 1 Basic Profile Dimensions 2 T
33、hread Series . . 3 Constants for Calculation Formulas of Thread Profile Dimensions 4 Limit Values, External Thread Root Radius, R . 5 Limiting Dimensions and Tolerances, UNJ Thread Form 6 Allowable Variations in Lead and Equivalent Change in Functional Diameter, UNJ Thread Form 7 Allowable Variation
34、s in 30 deg Basic Half-Angle of Screw Threads . Appendices A Symbols - UNJ Thread Dimensions and Tolerances B Tolerance Table . C Coating of Threads viii UNIFIED INCH SCREW THREADS (UNJ THREAD FORM) SECTION 1 GENERAL 1.1 Scope This Standard establishes the basic triangular pro- file for the UNJ thre
35、ad form, provides a system of designations, lists the standard series of diameter- pitch combinations for diameters from 0.600 to 6.000 in., and specifies limiting dimensions and tolerances. It specifies the characteristics of the UNJ inch series of threads having 0.1501 1P to 0.18042P designed ra-
36、dius at the root of the external thread, and also having the minor diameter of the external and internal threads increased above the ASME B1.l UN and UNR thread forms to accommodate the external thread maximum root radius. 1.2 Field of Application The UNJ screw thread is designed for aerospace inch
37、threaded parts, or for use on other highly stressed applications requiring high fatigue strength. For aero- space applications, only Classes 3A and 3B should be used. 1.3 Assembly Threads conforming to the UN profile (ASME B1.l) and the UNJ profile are not interchangeable because of possible interfe
38、rence between the UNJ external thread minor diameter and the UN internal thread minor diameter. However, the UNJ internal thread will assemble with the UN external thread. 1.4 Federal Government Use When this Standard is approved by the Department of Defense and federal agencies and is incorporated
39、into FED-STD-H28/4, Screw Thread Standards for Federal Services, Section 4, the use of this Standard by the federal government is subject to all the re- quirements and limitations of FED-STD-H28/4. 1.5 References The latest issues of the following documents form a part of this Standard to the extent
40、 specified herein. American National Standards ASME B1.l, Unified Inch Screw Threads (UN and UNR Thread Form) ASME B1.3M, Screw Thread Gaging Systems for Dimensional Acceptability ANWASME B1.7M, Nomenclature, Definitions, and Letter Symbols for Screw Threads ASME B1.23, Gages and Gaging for Unified
41、Inch J Series Screw Threads ASME B1.30M, Screw Threads - Standard Prac- tice for Calculating and Rounding Dimensions Proposed ASME Standard under development by The Amer- ican Society of Mechanical Engineers. UNIFIED INCH SCREW THREADS (UNJ THREAD FORM) SECTION 2 PROFILE OF THREAD 2.1 Basic Profile
42、The basic profile is the theoretical profile corre- sponding to the basic dimensions of the thread major diameter, pitch diameter, and minor diameter. Profile applies to an axial plane. The basic profile is shown in Fig. 1. 2.2 Basic Thread Profile Symbols The symbols used in the basic profile shown
43、 in Fig. 1 represent the following: D bsc = basic major diameter of internal thread D2 bsc = basic pitch diameter of internal thread Dl bsc = basic minor diameter of internal thread d bsc = basic major diameter of external thread d2 bsc = basic pitch diameter of external thread dl bsc = basic minor
44、diameter of external thread H = height of fundamental triangle P = pitch Appendix A provides a complete list of symbols applicable to the UNJ thread form. 2.3 Design Profiles The design profile for the internal thread at max- imum-material conditions is the same as the basic profile, except in pract
45、ice, the root is cleared above the basic major diameter, D bsc. See Fig. 2. The design profile for the external thread at max- imum-material condition for Class 3A is the basic profile with a radiused minor diameter tangent to the flanks for the upper limit profile. For Class 2A, an allowance is app
46、lied to the basic profile. The external thread crest may be flat, partially or corner rounded, tangent to the 0.125P flat. See Fig. 3. 2.4 Root Radius of the Thread 2.4.1 InternalThread. For internal threads, the profile of the actual root of the thread shall at no point be below the basic profile.
47、No root radius is specified. 2.4.2 External Thread. For external threads, the profile of the actual root of the thread shall lie within the root radius tolerance zone shown in Fig. 4. The limit dimensions of the root radius R as shown in Fig. 4 and their values are specified in Table 4. The profile
48、shall be a continuous smoothly blended nonreversing curve, no part of which shall have a radius of less than 0.15011P and which is tangent to the thread flanks at not less than 0.5625H basic thread depth. The profile may comprise tangent flank circular arcs that are tangent to the flanks and a flat
49、at the minor diameter provided that the minor diameter, d3, is within the zone established in Fig. 4. 2.4.3 Incomplete Threads. Unless otherwise specified, the runout threads on externally threaded parts shall be no less than 1, nor more than 2 pitches in length. The threads shall run-out onto the shank without any abrupt change in cross-sectional area. The root radius shall be no less than the minimum radius of the full thread section. UNIFIED INCH SCREW THREADS (UNJ THREAD FORM) FIG. 1 BASIC PROFILE UNIFIED INCH SCREW THREADS (UNJ THREAD FORM) GENERAL NOTE: Rounded crest is optional (S
