1、BRITISH STANDARD BS 811:1950 Incorporating Amendment issued July, 1951 Specification Cycle threadsBS811:1950 This British Standard, having been approved by the Mechanical Engineering Industry Standards Committee and endorsed by the Chairman of the Engineering Divisional Council, was published under
2、the authority of the General Council on24th May1950 BSI 03-1999 First published, October, 1938 First revision, May, 1950 Co-operating organizations The Mechanical Engineering Industry Standards Committee under whose supervision this British Standard was prepared consists of representatives from the
3、following Government departments and scientific and industrial organizations: Admiralty Air Ministry Associated Offices Technical Committee Association of Consulting Engineers (Incorporated) British Chemical Plant Manufacturers Association British Compressed Air Society British Electrical and Allied
4、 Manufacturers Association British Engineers Association British Internal Combustion Engine Manufacturers Association British Iron and Steel Federation British Railways Crown Agents for the Colonies Department of Scientific and Industrial Research Engineering Equipment Users Association Institute of
5、 Marine Engineers Institute of Petroleum Institution of Civil Engineers Institution of Gas Engineers Institution of Heating and Ventilating Engineers Institution of Mechanical Engineers Institution of Mechanical Engineers (Automobile Division) Institution of Production Engineers Locomotive Manufactu
6、rers Association Machine Tool Trades Association Ministry of Labour and National Service Ministry of Supply Ministry of Transport Ministry of Works Office of the High Commissioner for India War Office The Technical Committee on Screw Threads, which was entrusted with the preparation of this Standard
7、, has worked in close co-operation with the British Cycle and Motor Cycle Manufacturers and Traders Union. Amendments issued since publication Amd. No. Date CommentsBS811:1950 BSI 03-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Form of cycle thread 1 2 Dimensions
8、1 3 Classes of fit 2 4 Stainless steel components 3 5 Internal threads 3 6 Tolerances on effective diameter, pitch and flank angles 3 7 Designation of BS cycle threads 3 Appendix A BS Whitworth form threads for bolts, nuts and similar applications 15 Appendix B Bases of tolerances for cycle threads
9、16 Appendix C Tolerances on pitch and angle in relation to tolerance on effective diameters 17 Figure 1 Basic form of British Standard cycle thread 1 Figure 2 Tolerance zones 2 Table 1 Basic dimensions 3 Table 2 Bolts, Close class 4 Table 3 Bolts, Medium class 5 Table 4 Bolts, Free class 6 Table 5 N
10、uts, Close class 7 Table 6 Nuts, Medium class 8 Table 7 Nuts, Free class 9 Table 8 Basic dimensions 10 Table 9 Spokes, medium class 10 Table 10 Nipples, Medium class 11 Table 11 Basic dimensions 12 Table 12 Male threads, Medium class 13 Table 13 Female threads, Medium class 14 Table 14 Basic dimensi
11、ons 15 Table 15 British Standard whitworth from threads for bolts and nuts and similar applications (20 T.P.I. series) limits and tolerances 15 Table 16 Limits and tolerances 16BS811:1950 ii BSI 03-1999 Foreword In order to keep abreast of progress in the industries concerned, British Standards are
12、subject to periodical review. Suggestions for improvements will be recorded and in due course brought to the notice of the committees charged with the revision of the standards to which they refer. A complete list of British Standards, numbering over 4000, indexed and cross-indexed for reference, to
13、gether with an abstract of each standard, will be found in the Institutions Yearbook. NOTERecommendation on the application of the B.S.C. thread: In view of the fact that there is a close resemblance between the form of the B.S.C. thread and the form of Whitworth and B.A. threads, and that in certai
14、n sizes there is also a similarity between the pitches and diameters of the cycle thread and those of the Whitworth and B.A. series, the Institution most strongly recommends that the use of the B.S.C. thread be restricted to bolts and nuts and screwed parts to be used in cycle and motor cycle manufa
15、cture. Any introduction of the B.S.C. thread into general engineering would inevitably result in confusion due to the visual resemblance to, but lack of interchangeability with, threads of Whitworth or B.A. form. This British Standard for cycle threads has been prepared under the authority of the Me
16、chanical Engineering Industry Standards Committee and in close collaboration with the British Cycle and Motor Cycle Manufacturers and Traders Union. The standard was first issued in1938, and in that edition was limited to the standardization of the thread form and the basic dimensions. This present
17、edition reproduces the former thread form and basic dimensions unaltered, and has been prepared to include tables of limits and tolerances. The form of thread was first formulated by the Cycle Engineers Institute in1902 to provide a thread of suitable design and mechanical strength for the bolts, nu
18、ts, nipples, spokes, and other threaded parts of cycles and motor cycles. In 1933 the British Cycle and Motor Cycle Manufacturers and Traders Union approached the British Standards Institution for the recognition of this thread as a British Standard. The first edition of the British Standard did not
19、, however, attempt to include all the many pitches and diameters which had been or were then in use. The C.E.I. thread system would appear to have been peculiar in that, as originally developed, it included a series of threads applicable to any size of stock, rather than organized and progressive si
20、zes, and in practice this had resulted in a considerable diversity of diameters and associated pitches. Since there appeared to be no justification for this complexity, the British Standard, in its first edition, standardized only a selection of the more commonly used sizes. These sizes have since b
21、ecome established as the threads in regular use in the cycle and motor cycle industries, and they are perpetuated in this second edition. The tolerances, other than those for the threads on spokes and nipples, have been derived from similar formulae to those adopted for the tolerances in the1940 edi
22、tion of BS84, “Screw threads of Whitworth form,” the appropriate correction being made for the difference between the angles of the Whitworth thread and the cycle thread. The bases for calculating the tolerances are given for reference in Appendix B.BS 811:1950 BSI 03-1999 iii The first edition of t
23、his standard included, in deference to usage at that time, a20t.p.i. series as an alternative to the normal series for bolts and nuts and similar applications, but the continuance of that series was not recommended. In the present edition this20t.p.i. series is omitted from the tables of threads hav
24、ing the form of the cycle thread, but in view of the use in the cycle industry of this pitch series with a Whitworth form thread the appropriate dimensions are given in Appendix A. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards a
25、re responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv, pages1to17 and a back cover. This standard has been updated (see cop
26、yright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.iv blankBS 811:1950 BSI 03-1999 1 1 Form of cycle thread The basic form of the British Standard cycle thread shall be as shown in Figure 1. 2 Dimensions The basic dimensions
27、and limits and tolerances for British Standard cycle threads shall be as given in Table 1 to Table 13. Table 1 to Table 7 provide for the threads for bolts and nuts and similar applications. NOTEIt is a customary practice in the cycle industry to use a20t.p.i. series of Whitworth form threads as an
28、alternative to the cycle form thread series given in Table 1 to Table 7. Full details of Whitworth form threads are given in BS84:1940, “Screw threads of Whitworth form,” but for convenience the relevant dimensions are reproduced in Appendix A, Table 14 to Table 16. Table 8 to Table 10 provide for t
29、hreads for spokes and nipples. They are right hand. The spoke threads are normally rolled, and the basic effective diameter has been taken as the nominal size of the end portion of the spoke on which the thread is rolled: it is to be noted that this diameter is not necessarily that of the body of th
30、e spoke. Table 11 to Table 13 provide for a number of threads used in current practice for the particular applications stated. The bases of the tolerances are explained in Appendix B. Figure 2 illustrates the tolerance zones on the threads. Figure 1 Basic form of British Standard cycle threadBS811:1
31、950 2 BSI 03-1999 The limits given in the tables represent the acceptance limits for the finished components. It is to be appreciated that if the components are to be plated or hardened after machining it may be necessary for them to be machined to modified limits so that the components, as finally
32、finished, may be within the limits given in the tables, but see exception stated in Clause4. 3 Classes of fit The following classes of accuracy, or fit, are provided: B.S.C. bolts and nuts, Close, Medium and Free classes. B.S.C. spokes and nipples, Medium class. B.S.C. threads for special applicatio
33、ns, Medium class. B.S.W. bolts and nuts (20 t.p.i. series), Medium class. These classes of accuracy may be described as follows: Close class. The close class applies to screw threads requiring a fine, snag fit. This grade of fit is obtainable consistently only by the use of the highest quality screw
34、ing tools supported by a very efficient system of gauging and inspection. It is recommended only for special work where refined accuracy of pitch and thread form are particularly required. Medium class. The medium class applies to the better class of ordinary interchangeable screw threads. Free clas
35、s. The free class applies to the great bulk of screw threads of ordinary commercial quality. The choice between the three classes for a particular purpose rests with the designer. The two threads of any mating pair need not necessarily be made to the same class, and in some circumstances it may be d
36、esirable to specify their manufacture to different classes. For example, for the special bolts and nuts and threaded parts used on motor cycle power units the close class for bolts (external threads) and the medium class for nuts (internal threads) would be appropriate; for ordinary bolts and nuts a
37、nd threaded parts on power units and the bolts and nuts for motor cycle and cycle frame construction, medium class for bolts (external threads) and free class for nuts (internal threads) would be adequate. NOTENone of the classes in this specification apply to screw threads which have to mate with a
38、n interference fit. Figure 2 Tolerance zonesBS 811:1950 BSI 03-1999 3 4 Stainless steel components In view of the tendency for closely fitting threaded components of stainless steel to seize when tightened together, it is recommended that the maximum permissible size for all stainless steel bolts an
39、d externally threaded components should be0.001 in. below their basic size. The same manufacturing tolerances should be allowed, however, on these components as for components of other materials. 5 Internal threads No tolerance is laid down for the major diameter of internal threads. It is recommend
40、ed, however, that the radius at the major diameter of internal threads should never be less than one-half the standard radius for the pitch of thread concerned. The minor diameter tolerances are such as to permit of the use of a tapping drill of ample size to prevent binding at the root of the tap.
41、It is to be understood that if full advantage is taken of the generous tolerances allowed on the minor diameters of internal threads, the crests of these threads will be flat. 6 Errors in pitch and flank angles The effective diameter tolerances are intended to cover not only errors in the simple eff
42、ective diameter but also the effects of all errors present in the pitch and the flank angles. NOTEA detailed explanation of the effect of errors in pitch and angle in relation to the tolerance on effective diameter is given in Appendix C. 7 Designation of British Standard cycle threads It is recomme
43、nded that British Standard cycle threads be referred to on drawings, etc., by their basic major diameter and number of threads per inch, followed by the abbreviation “BSC” and the class. If a thread is left-hand, the symbol “LH” should follow the designation. Example: 26. BSC Free. 1.290 24. BSC Med
44、. LH Table 1 British Standard cycle threads for bolts and nuts and similar applications Basic Dimensions 1 2 3 4 5 6 7 Nominal diameter of screw No. of threads per inch Pitch Depth of thread Basic diameters Major Effective Minor in. in. in. in. in. in. 40 0.02500 0.0133 0.1250 0.1117 0.0984 32 0.031
45、25 0.0166 0.1563 0.1397 0.1231 32 0.03125 0.0166 0.1875 0.1709 0.1543 26 0.03846 0.0205 0.2188 0.1983 0.1778 26 0.03846 0.0205 0.2500 0.2295 0.2090 26 0.03846 0.0205 0.2813 0.2608 0.2403 26 0.03846 0.0205 0.3125 0.2920 0.2715 26 0.03846 0.0205 0.3750 0.3545 0.3340 26 0.03846 0.0205 0.4375 0.4170 0.3
46、965 26 0.03846 0.0205 0.5000 0.4795 0.4590 26 0.03846 0.0205 0.5625 0.5420 0.5215 26 0.03846 0.0205 0.6250 0.6045 0.5840 26 0.03846 0.0205 0.6875 0.6670 0.6465 26 0.03846 0.0205 0.7500 0.7295 0.7090 1 / 8 5 / 32 3 / 16 7 / 32 1 / 4 9 / 32 5 / 16 3 / 8 7 / 16 1 / 2 9 / 16 5 / 8 11 / 16 3 / 4BS811:195
47、0 4 BSI 03-1999 Table 2 British Standard cycle threads for bolts and nuts and similar applications Limits and tolerances Bolts Close class 1 2 3 4 5 6 7 8 9 10 11 Nom. dia. t.p.i. Major diameter Effective diameter Minor diameter max. tol. min. max. tol. min. max. tol. min. in. in. in. in. in. in. in
48、. in. in. in. 40 0.1250 0.0033 0.1217 0.1117 0.0017 0.1100 0.0984 0.0038 0.0946 32 0.1563 0.0037 0.1526 0.1397 0.0019 0.1378 0.1231 0.0042 0.1189 32 0.1875 0.0037 0.1838 0.1709 0.0019 0.1690 0.1543 0.0042 0.1501 26 0.2188 0.0041 0.2147 0.1983 0.0021 0.1962 0.1778 0.0046 0.1732 26 0.2500 0.0042 0.245
49、8 0.2295 0.0022 0.2273 0.2090 0.0047 0.2043 26 0.2813 0.0043 0.2770 0.2608 0.0023 0.2585 0.2403 0.0048 0.2355 26 0.3125 0.0044 0.3081 0.2920 0.0024 0.2896 0.2715 0.0049 0.2666 26 0.3750 0.0045 0.3705 0.3545 0.0025 0.3520 0.3340 0.0050 0.3290 26 0.4375 0.0047 0.4328 0.4170 0.0027 0.4143 0.3965 0.0052 0.3913 26 0.5000 0.0048 0.4952 0.4795 0.0028 0.4767 0.4590 0.0053 0.4537 26 0.5625 0.0049 0.5576 0.5420 0.0029 0.5391 0.5215 0.0054 0.5161 26 0.6250 0.0050 0.6200 0.6045 0.0030 0.6015 0.5840 0.0055 0.5785 26 0.687
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