BS 84-2007 Parallel screw threads of nWhitworth form – nRequirements《惠氏螺纹牙样的平行螺纹 要求》.pdf

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1、BS 84:2007Parallel screw threads of Whitworth form RequirementsICS 21.040.20NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2

2、007ISBN 978 0 580 57923 3The following BSI references relate to the work on this standard:Committee reference FME/9Draft for comment 07/30158483 DCPublication historyFirst published as BS 84:1918 and BS 92:1919Second edition as BS 84 (incorporating BS 92) May 1940Third edition, September 1956Fourth

3、edition, November 2007Amendments issued since publicationAmd. no. Date Text affectedBS 84:2007 BSI 2007 iBS 84:2007ContentsForeword iii1 Scope 12 Normative references 13 Terms and definitions and symbols 14 Profile of Whitworth screw thread 25 Tolerance classes of external and internal threads 36 Li

4、mits of sizes, and tolerances, for uncoated B.S.W. and B.S.F. threads 37 Limits of size, and tolerances, for B.S.W. and B.S.F. coated threads 48 Stainless steel external threads 59 Selected thread series 610 Designation of screw threads of Whitworth form 811 Gauges 8AnnexesAnnex A (normative) Trunca

5、ted Whitworth form threads with flat crests 40Annex B (informative) Bases of tolerances and allowances for Whitworth form screw threads 47Annex C (informative) Tolerances on pitch and flank angle in relation to tolerance on effective diameter 50Annex D (informative) Form of the crests of Whitworth t

6、hreads 53Annex E (normative) Limits and tolerances for close class internal threads for special uses 55Bibliography 58List of figuresFigure 1 Basic form of Whitworth thread 9Figure 2 Effective diameter tolerance zones of recommended combinations of classes of internal and external Whitworth form thr

7、eads 10Figure 3 Tolerance zones for a close class external thread and a medium class internal thread in B.S.W. (20 t.p.i.) illustrated 11Figure 4 Tolerance zones for a medium class external thread with allowance and a normal class internal thread in B.S.W. (20 t.p.i.) illustrated 12Figure 5 Toleranc

8、e zones for a free class external thread with allowance and a normal class internal thread in B.S.W. (20 t.p.i.) illustrated 13Figure 6 Effective diameter tolerance zones for external and internal threads, uncoated or before coating, and after coating (c.f. Figure 2) of sizes in nominal size and sma

9、ller 14Figure A.1 Tolerance zones for truncated Whitworth threads (close class external thread and medium class internal thread) in B.S.W. (20 t.p.i.) illustrated 43Figure D.1 Crest forms resulting from different production methods 54List of tablesTable 1 Coarse thread series (B.S.W.) Basic sizes 15

10、Table 2 Coarse thread series (B.S.W.) External threads Close class Limits and tolerances 1614-14-14-34-14-BS 84:2007ii BSI 2007Table 3 Coarse thread series (B.S.W.) Internal threads Medium class Limits and tolerances 17Table 4 Coarse thread series (B.S.W.) External threads Medium class Limits and to

11、lerances 18Table 5 Coarse thread series (B.S.W.) Internal threads Normal class Limits and tolerances 19Table 6 Coarse thread series (B.S.W.) External threads Free class Limits and tolerances 20Table 7 Fine thread series (B.S.F.) Basic sizes 21Table 8 Fine thread series (B.S.F.) External threads Clos

12、e class Limits and tolerances 22Table 9 Fine thread series (B.S.F.) Internal threads Medium class Limits and tolerances 23Table 10 Fine thread series (B.S.F.) External threads Medium class Limits and tolerances 24Table 11 Fine thread series (B.S.F.) Internal threads Normal class Limits and tolerance

13、s 25Table 12 Fine thread series (B.S.F.) External threads Free class Limits and tolerances 26Table 13A Selected thread series (Whit. S.) Preferred diameters and pitches Fractional sizes 27Table 13B Selected thread series (Whit. S.) Preferred diameters and pitches Decimal sizes 31Table 14 Selected th

14、read series (Whit. S.) and non-standard threads Depths of thread for various pitches 34Table 15 Selected thread series (Whit. S.) and non-standard threads External threads Medium and free class Allowances 37Table 16 Selected thread series (Whit. S.) and non-standard threads External threads Close cl

15、ass Tolerances 37Table 17 Selected thread series (Whit. S.) and non-standard threads Internal threads Medium class Tolerances 38Table 18 Selected thread series (Whit. S.) and non-standard threads External threads Medium class Tolerances 38Table 19 Selected thread series (Whit. S.) and non-standard t

16、hreads Internal threads Normal class Tolerances 39Table 20 Selected thread series (Whit. S.) and non-standard threads External threads Free class Tolerances 39Table A.1 Truncated threads Whitworth form Basic data 44Table A.2 Truncated threads British Standard Whitworth (B.S.W.) series External and i

17、nternal threads All classes Limits and tolerances 45Table A.3 Truncated threads British Standard Fine (B.S.F.) series External and internal threads All classes Limits and tolerances 46Table E.1 Coarse thread series (B.S.W.) Internal threads Close class Limits and tolerances 55Table E.2 Fine thread s

18、eries (B.S.F.) Internal threads Close class Limits and tolerances 56Table E.3 Selected and non-standard threads Internal threads Close class Tolerances 57Summary of pagesThis document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 58, an inside back cover and a back cover.

19、 BSI 2007 iiiBS 84:2007ForewordPublishing informationThis British Standard is published by BSI and came into effect on 30 November 2007. It was prepared by Subcommittee SFTSE/1, Screws and fasteners technical specification committee, under the authority of Technical Committee FME/9, Nuts, bolts and

20、accessories. A list of organizations represented on this committee can be obtained on request to its secretary.SupersessionThis British Standard supersedes BS 84:1956, which is withdrawn.Relationship with other publicationsThis British Standard is intended for use with BS 919-2, which specifies the

21、corresponding screw gauges.Information about this documentThis British Standard has been fully revised to bring it up to date.This British standard includes tables of basic sizes, limits and tolerances for British Standard Whitworth (B.S.W.) and British Standard Fine (B.S.F.) screw threads. In addit

22、ion it provides a “Selected thread” series of recommended diameter/pitch combinations for use in applications where the standard coarse (B.S.W.) and fine (B.S.F.) series have insufficiently fine pitches.An allowance (minimum clearance) is provided on certain classes of external threads of sizes up t

23、o and including in diameter; the recommended combinations of classes of internal threads and external threads include internal threads having larger effective diameter tolerances than the corresponding sizes of external threads. Three tolerance classes are specified for external threads, close, medi

24、um and free. The allowance is provided for medium class and free class external threads by specifying maximum external thread limits below the basic size. The purpose of this allowance is to provide for the threads to be coated if necessary, the coating encroaching within the allowance; it is also i

25、ntended to permit easy assembly of maximum material condition (MMC) external threads and internal threads, thus facilitating the use of torque wrenches. Two tolerance classes of internal threads are specified, medium and normal. Close class internal threads are now non-preferred but, in view of thei

26、r usage in the past and for special uses, limits and tolerances for these are specified in Annex E.No change has been made in the general three-part formula used as a basis for tolerancing effective diameters, and the formulae used for tolerancing the other thread elements also remain unchanged from

27、 those in BS 84:1956; the reason for this is to minimize any changes in the sizes of the gauges used to control the size of the finished work.The table of recommended diameter/pitch combinations for screw threads in the “Selected thread” series follows very closely the corresponding table (Table 37)

28、 in BS 1580-1.34-BS 84:2007iv BSI 2007The foreword of BS 84:1956 ended with the following statement. “In conclusion it may be asked why the revision of this standard has been undertaken in view of the standardization of the Unified thread in BS 1580. The reason is that Whitworth threads will undoubt

29、edly continue to be used for many years, especially on replacements or spare parts.” The present revision of BS 84 has been undertaken because, fifty years on, this continues to be the case.Hazard warningsPresentational conventionsThe provisions of this standard are presented in roman (i.e. upright)

30、 type. Its requirements are expressed in sentences in which the principal auxiliary verb is “shall”.Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not

31、purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.WARNING. Attention is drawn to the fact that, with the different screw thread forms available, there is th

32、e possibility of a mismatch, which is potentially hazardous. It is the responsibility of the designer of the end product to ensure that this possibility is reduced to a minimum. For further information on mismatches of screw thread systems see PD 6494. BSI 2007 1BS 84:20071 ScopeThis British Standar

33、d specifies limits of sizes, and tolerances, for single start parallel screw threads of Whitworth form, for general engineering use. It is not applicable to threads for threaded pipe joints, screw threads associated with interference fits, such as those on the “metal ends” of studs and in the corres

34、ponding tapped holes, or to screw threads which are to be subjected to high temperatures.This standard specifies the following thread series:a) a coarse thread series, the British Standard Whitworth (B.S.W.) series, with nominal diameters in the range in to 6 in.b) a fine thread series, the British

35、Standard fine (B.S.F.) series, with nominal diameters in the range in to 4 in.NOTE The tables of limits and tolerances for the B.S.F. series extend up to the 3 in size only, since nominal sizes above 3 in are rarely used.c) a supplementary selected thread (WHIT. S.) series with nominal diameters fro

36、m in to 7 in.d) a truncated Whitworth form series (specified in Annex A).This British Standard specifies limits of sizes, and tolerances, of uncoated threads and also for metal coated threads (including threads coated with nickel, tin or zinc) with a thickness of coating of the order of 0.000 2 in.

37、It is not applicable to heavily coated threads (i.e. threads with a coating thickness above 0.000 35 in).NOTE Supplementary information is given in Annex B, Annex C and Annex D.2 Normative references The following referenced documents are indispensable for the application of this document. For dated

38、 references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.BS 919-2, Screw gauge limits and tolerances Part 2: Specification for gauges for screw threads of Whitworth and B.A. formsBS 6528:1984, Glossary of te

39、rms for cylindrical screw threads3 Terms and definitions and symbols3.1 Terms and definitionsFor the purposes of this British Standard the terms and definitions given in BS 6528:1984 and the following apply.3.1.1 effective diameterdiameter of the pitch cylinderNOTE 1 This is the “simple” effective d

40、iameter, as distinct from the “virtual” effective diameter (see 3.1.2).NOTE 2 Also known as the pitch diameter.18-316-14-14-BS 84:20072 BSI 20073.1.2 virtual effective diametereffective diameter of an imaginary thread of perfect pitch and flank angle, having the full depth of flanks, but clear at th

41、e crests and roots, which would just assemble with the actual thread over the prescribed length of engagementNOTE The “virtual” effective diameter exceeds the simple effective diameter in the case of an external thread, but is less than the simple effective diameter in the case of an internal thread

42、, by an amount corresponding to the combined diametral effects due to any errors in the pitch and/or the flank angles of the thread.3.2 SymbolsFor the purposes of this British Standard the following symbols apply.NOTE 1 These are repeated from BS 6528 for the convenience of users of this standard.D

43、major diameter of internal thread D1minor diameter of internal threadD2effective diameter of internal thread (see Note 2)d major diameter of external threadd1minor diameter of external threadd2effective diameter of external thread (see Note 2)H height of fundamental triangleP pitchNOTE 2 These are t

44、he symbols given for pitch diameter in BS 6528.4 Profile of Whitworth screw threadThe basic profile, and the design profile, of the Whitworth thread shall be as shown in Figure 1. The thread shall be a symmetrical V-thread in which the angle between the flanks, measured in an axial plane, is 55, one

45、-sixth of the V is truncated at the top and bottom, the thread is rounded equally at crests and roots by circular arcs blending tangentially with the flanks and the theoretical depth of the thread is 0.640 327 times the nominal pitch. NOTE The basic thread depths specified in this standard have been

46、 rounded to the nearest 0.000 1 in. BSI 2007 3BS 84:20075 Tolerance classes of external and internal threadsExternal threads and internal threads shall be of one of the following tolerance classes:a) close class external threads;NOTE 1 This class of threads is for use where a close fit is required.

47、Threads of this class are obtainable consistently only by the use of the highest quality production equipment supported by a particularly efficient system of gauging and inspection. They are intended for special work where a high degree of accuracy of pitch and thread form are particularly required.

48、NOTE 2 Limits and tolerances for close class internal threads for special uses are given in Annex E.b) medium class external threads and internal threads; NOTE 3 This tolerance class is for ordinary use, but the accuracy of pitch and thread form is greater than that for free class and normal class threads.c) free class external threads; NOTE 4 This tolerance class is for ordinary commercial use.d) normal class internal threads. NOTE 5 This tolerance class is for ordinary commercial use.NOTE 6 This class of internal threads is intended for use with medium cla