1、BRITISH STANDARD BS 1157:1975 Recommendations for Tapping drill sizes for use with fluted taps UDC 621.952.6.02:621.993BS1157:1975 These recommendations, havingbeen approved by the Mechanical Engineering IndustryStandards Committee,were published underthe authority of the Executive Board on 30Septem
2、ber1975 BSI 08-1999 First published February1944 First revision October1953 Second revision July1965 Third revision September1975 The following BSI references relate to the work on these recommendations: Committee reference MEE/1, MEE/1/20 Draft for comment72/33476 DC ISBN 0 580 08685 2 Co-operating
3、 organizations The Mechanical Engineering Industry Standards Committee, under whose supervision these recommendations were prepared, consists of representatives from the following Government departments and scientific and industrial organizations: The Government departments and scientific and indust
4、rial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of these recommendations: Associated Offices Technical Committee Department of Trade Association of Consulting Engineers Electricity Su
5、pply Industry in England and Association of Hydraulic Equipment Wales Manufacturers Ltd. Engineering Equipment Users Association Association of Mining Electrical and Federation of Manufacturers of Construction Mechanical Engineers Equipment and Cranes British Compressed Air Society Institution of Ga
6、s Engineers British Electrical and Allied Manufacturers Institution of Heating and Ventilating Association* Engineers British Gas Corporation Institution of Mechanical Engineers British Gear Manufacturers Association Institution of Plant Engineers British Internal Combustion Engine Institution of Pr
7、oduction Engineers* Manufacturers Association* London Transport Executive* British Mechanical Engineering Confederation Machine Tool Trades Association British Pump Manufacturers Association Ministry of Defence* British Steel Corporation National Coal Board British Steel Industry Process Plant Assoc
8、iation Crown Agents for Oversea Governments and Railway Industry Association of Great Britain* Administrations Royal Institute of British Architects Department of Employment (HM Factory Society of Motor Manufacturers and Traders Inspectorate) Ltd.* Department of the Environment Telecommunication Eng
9、ineering and Department of Industry Manufacturing Association* Department of Industry National Engineering Laboratory* Agricultural Engineers Association Motor Cycle Association of Great Britain British Bolt, Nut, Screw and Rivet Federation National Association of Marine Engine British Railways Boar
10、d Builders Business Equipment Trade Association Screw Thread Tool Manufacturers Association Electronic Engineering Association Society of British Aerospace Companies Ltd. Fasteners Turned Parts Institute Socket Screw Manufacturers Association Gauge Toolmakers Association Twist Drill Association Amen
11、dments issued since publication Amd. No. Date of issue CommentsBS1157:1975 BSI 08-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 0 Introduction 1 1 Scope 2 2 References 2 Appendix A Alternative tapping drill sizes 15 Figure 1 Whitworth and British Association (BA) thr
12、ead forms 2 Figure 2 ISO metric and Unified thread forms 2 Table 1 ISO metric thread (coarse pitch series) 3 Table 2 ISO metric thread (fine pitch series:0.25mm, 0.35mm, 0.50mm and0.75mm) 4 Table 3 ISO metric thread (fine pitch series:1.00mm and1.25mm) 5 Table 4 ISO metric thread (fine pitch series:
13、1.5mm) 6 Table 5 ISO metric thread (fine pitch series:2.0 mm) 7 Table 6 ISO metric thread (fine pitch series:3.0mm) 7 Table 7 ISO metric thread (fine pitch series:4.0mm) 8 Table 8 Unified coarse thread (UNC): number sizes 8 Table 9 Unified coarse thread (UNC): fractional inch sizes 9 Table 10 Unifie
14、d fine thread (UNF): number sizes 9 Table 11 Unified fine thread (UNF): fractional inch sizes 10 Table 12 British Standard parallel pipe thread (R p ) 10 Table 13 British Standard parallel pipe thread (G) 11 Table 14 British Standard taper pipe thread (R c ) 11 Table 15 British Standard Whitworth th
15、read (BSW) 12 Table 16 British Standard fine thread (BSF) 13 Table 17 British Association thread (BA) 14 Table 18 ISO metric thread (coarse pitch series): alternative sizes 15 Table 19 ISO metric thread (fine pitch series:0.25mm, 0.35mm, 0.50mm and0.75mm): alternative sizes 16 Table 20 ISO metric th
16、read (fine pitch series:1.00mm and1.25mm): alternative sizes 16 Table 21 ISO metric thread (fine pitch series:1.5mm): alternative sizes 17 Table 22 ISO metric thread (fine pitch series:2.0mm): alternative sizes 17 Table 23 ISO metric thread (fine pitch series:3.0mm): alternative sizes 17 Table 24 Un
17、ified coarse thread (UNC): number sizes: alternative sizes 17 Table 25 Unified coarse thread (UNC): fractional inch sizes: alternative sizes 18 Table 26 Unified fine thread (UNF): number sizes: alternative sizes 18 Table 27 Unified fine thread (UNF): fractional inch sizes: alternative sizes 18 Table
18、 28 British Standard parallel pipe thread (R P ): alternative sizes 19 Table 29 British Standard parallel thread (G): alternative sizes 19 Table 30 British Standard Whitworth thread (BSW): alternative sizes 19 Table 31 British Standard fine thread (BSF): alternative sizes 20 Table 32 British Associa
19、tion thread (BA): alternative sizes 21 Publications referred to Inside back coverBS1157:1975 ii BSI 08-1999 Foreword These recommendations, prepared under the authority of the Mechanical Engineering Industry Standards Committee, give recommended metric sizes of tapping drills which are regularly sto
20、cked for the standard sizes and types of screw threads in common use. The application of this publication does not absolve a manufacturer of the responsibility for producing a screw thread in accordance with the relevant screw thread standard. BS1157 was first published in1953 and revised in1965. Th
21、is latest edition has been published in order that it is in agreement with International Standard ISO2306 “Drills for use prior to tapping screw threads”. This has enabled the provisions of BS1157, Supplement No.1:1967 “Table 10 toTable 16. Tapping drill sizes for ISO metric screw threads in accorda
22、nce with BS3643”, to be incorporated in the body of these recommendations. It should be noted that all the drill diameters are shown in BS328 “Twist drills and combined drills and countersinks”, Part1 “Twist drills”, either as standard sizes or as specials for use when tapping holes. Appendix A show
23、s alternative metric sizes of drills where such sizes are available as standard. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself
24、confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 22, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indic
25、ated in the amendment table on the inside front cover.BS1157:1975 BSI 08-1999 1 0 Introduction The diameter of a hole produced by a drill depends to some extent upon the degree of accuracy to which the drill point is ground, the material being drilled, the lubricant used, and the alignment, feed and
26、 speed of the operation. When tapping relatively soft material, there is a tendency for the material to be squeezed down towards the root of the tap threads and in such cases the minor diameter of the tapped hole may become smaller than the diameter of the drill used. The tendency is very much less
27、with harder materials, and in some cases is entirely absent. The larger the drilled hole, within the relevant nut minor diameter tolerance, the more economical tapping becomes, and the risk of tap breakage is reduced. With the foregoing points in mind,Table 1 toTable 14 have been prepared as a guide
28、 to drilling prior to conventional tapping. However, it is realized that users may find it beneficial to choose their own drill diameters for certain applications. Even in these instances, stocked diameter drills should be used whenever possible. SeeAppendix A. It should be noted that a fluteless ta
29、p will require, for the same screw thread, a different size of twist drill from that given in this document and that this type of tap is not therefore covered by these recommendations. For the convenience of the users who wish to choose their own drill sizes for special purposes, the limits of size
30、of the nut minor diameters are given for each size and type of thread. For general guidance the majority of tables give comparable figures of the theoretical extent of engagement of the nut and bolt threads resulting from the use of the stipulated drill size. For purposes of calculation it has been
31、assumed that the major diameter of the bolt is basic size and that the minor diameter of the nut is equal to the nominal diameter of the drill concerned. Owing to the basic difference in thread form, however, between Whitworth and BA threads (seeFigure 1) as compared with ISO metric and Unified thre
32、ads (seeFigure 2), the maximum possible depth of engagement (100%) has a different interpretation; the latter thread profiles having a truncated nut as the design form and the former threads having engagement of the complete profile. It is, therefore, based on the depth of the external thread in the
33、 maximum metal condition, it being considered that the figure required by the user of these recommendations is that of engagement compared with the full form of the external thread rather than comparison with a maximum possible engagement already substantially reduced because of the truncated nut of
34、 a particular thread design. It is felt that a common basis of the depth of the external thread affords the only possible means of providing truly comparable figures, but it is not intended to give a comparison of efficiency between one thread form and another. In the selection of drill sizes the ai
35、m has been to specify drills which will afford at least70% engagement between the bolt and nut. The relationship, however, between the maximum minor diameter of the nut and the basic major diameter of the bolt, in the cases of most Unified threads below : in diameter, affords an engagement of less t
36、han the70% approved minimum. Due, therefore, to the relatively high maximum minor diameters, the drill sizes afford a fairly low engagement in these ranges. Percentage depth of engagement = (nom. (basic major) dia. of threaddrill dia.) 2 (depth of external thread) -100 BS1157:1975 2 BSI 08-1999 1 Sc
37、ope These recommendations give drill sizes, covered by BS328-1, for use prior to tapping the threads indicated. Table 1 toTable 14 cover preferred thread forms andTable 15 toTable 17 cover non-preferred forms. Appendix A covers alternative tapping drill sizes. 2 References The titles of the British
38、Standards referred to in these recommendations are listed on the inside back cover. Whitworth form threads, h s= 0.64033p BA form threads, h s= 0.60000p Figure 1 Whitworth and British Association (BA) thread forms h s= 0.61344p Figure 2 ISO metric and Unified thread formsBS1157:1975 BSI 08-1999 3 Ta
39、ble 1 ISO metric thread (coarse pitch series) a Dimensions in millimetres except where otherwise stated. Nominal diameter of thread Pitch (p) Minor diameter of nut Depth of external thread (0.61344p) Drill diameter Theoretical radial engagement with external thread Maximum class5H Maximum class6H Ma
40、ximum class7H Minimum classes5H, 6H,7H % M 1.0 M 1.1 M 1.2 M 1.4 M 1.6 M 1.8 0.25 0.25 0.25 0.30 0.35 0.35 0.785 0.885 0.985 1.142 1.301 1.501 1.160 1.321 1.521 0.729 0.829 0.929 1.075 1.221 1.421 0.1534 0.1534 0.1534 0.1840 0.2147 0.2147 0.75 0.85 0.95 1.10 1.25 1.45 81.5 81.5 81.5 81.5 81.5 81.5 M
41、 2.0 M 2.2 M 2.5 M 3.0 M 3.5 M 4.0 0.40 0.45 0.45 0.50 0.60 0.70 1.657 1.813 2.113 2.571 2.975 3.382 1.679 1.838 2.138 2.599 3.010 3.422 2.639 3.050 3.466 1.567 1.713 2.013 2.459 2.850 3.242 0.2454 0.2760 0.2760 0.3067 0.3681 0.4294 1.60 1.75 2.05 2.50 2.90 3.30 81.5 81.5 81.5 81.5 81.5 81.5 M 4.5 M
42、 5.0 M 6.0 M 7.0 M 8.0 M 9.0 0.75 0.80 1.00 1.00 1.25 1.25 3.838 4.294 5.107 6.107 6.859 7.859 3.878 4.334 5.153 6.153 6.912 7.912 3.924 4.384 5.217 6.217 6.982 7.982 3.688 4.134 4.917 5.917 6.647 7.647 0.4601 0.4908 0.6134 0.6134 0.7668 0.7668 3.70 4.20 5.00 6.00 6.80 7.80 86.8 81.5 81.5 81.5 78.5
43、78.5 M 10 M 11 M 12 M 14 M 16 1.50 1.50 1.75 2.00 2.00 8.612 9.612 10.371 12.135 14.135 8.676 9.676 10.441 12.210 14.210 8.751 9.751 10.531 12.310 14.310 8.376 9.376 10.106 11.835 13.835 0.9202 0.9202 1.0735 1.2269 1.2269 8.50 9.50 10.20 12.00 14.00 81.5 81.5 83.7 81.5 81.5 M 18 M 20 M 22 M 24 M 27
44、M 30 M 33 2.50 2.50 2.50 3.00 3.00 3.50 3.50 15.649 17.649 19.649 21.152 24.152 26.661 29.661 15.744 17.744 19.744 21.252 24.252 26.771 29.771 15.854 17.854 19.854 21.382 24.382 26.921 29.921 15.294 17.294 19.294 20.752 23.752 26.211 29.211 1.5336 1.5336 1.5336 1.8403 1.8403 2.1470 2.1470 15.50 17.5
45、0 19.50 21.00 24.00 26.50 29.50 81.5 81.5 81.5 81.5 81.5 81.5 81.5 M 36 M 39 M 42 M 45 M 48 M 52 M 56 4.00 4.00 4.50 4.50 5.00 5.00 5.50 32.145 35.145 37.659 40.659 43.147 47.147 50.646 32.270 35.270 37.799 40.799 43.297 47.297 50.796 32.420 35.420 37.979 40.979 43.487 47.487 50.996 31.670 34.670 37
46、.129 40.129 42.587 46.587 50.046 2.4538 2.4538 2.7605 2.7605 3.0672 3.0672 3.3739 32.00 35.00 37.50 40.50 43.00 47.00 50.50 81.5 81.5 81.5 81.5 81.5 81.5 81.5 a This thread form is covered by BS3643-2.BS1157:1975 4 BSI 08-1999 Table 2 ISO metric thread (fine pitch series) a : 0.25mm,0.35mm,0.50mm an
47、d0.75mm) Dimensions in millimetres except where otherwise stated. Nominal diameter of thread Pitch (p) Minor diameter of nut Depth of external thread (0.61344p) Drill diameter Theoretical radial engagement with external thread Maximum class5H Maximum class6H Maximum class7H Minimum classes5H, 6H,7H
48、% M 2.0 M 2.2 0.25 0.25 1.785 1.985 1.729 1.929 0.1534 0.1534 1.75 1.95 81.5 81.5 M 2.5 M 3.0 M 3.5 0.35 0.35 0.35 2.201 2.701 3.201 2.221 2.721 3.221 2.121 2.621 3.121 0.2147 0.2147 0.2147 2.15 2.65 3.15 81.5 81.5 81.5 M 4.0 M 4.5 M 5.0 M 5.5 0.50 0.50 0.50 0.50 3.571 4.071 4.571 5.071 3.599 4.099
49、4.599 5.099 3.639 4.139 4.639 5.139 3.459 3.959 4.459 4.959 0.3067 0.3067 0.3067 0.3067 3.50 4.00 4.50 5.00 81.5 81.5 81.5 81.5 M 6.0 M 7.0 M 8.0 M 9.0 M 10.0 M 11.0 0.75 0.75 0.75 0.75 0.75 0.75 5.338 6.338 7.338 8.338 9.338 10.338 5.378 6.378 7.378 8.378 9.378 10.378 5.424 6.424 7.424 8.424 9.424 10.424 5.188 6.188 7.188 8.188 9.188 10.188 0.4601 0.4601 0.4601 0.4601 0
