BS 1157:1975

Co-operating organizations
Foreword
Recommendations
0 Introduction
1 Scope
2 References
Appendix
A Alternative tapping drill sizes
Tables
1 ISO metric thread (coarse pitch series)
2 ISO metric thread (fine pitch series: 0.25 mm, 0.35
    mm, 0.50 mm and 0.75 mm)
3 ISO metric thread (fine pitch series: 1.00 mm and
    1.25 mm)
4 ISO metric thread (fine pitch series: 1.5 mm)
5 ISO metric thread (fine pitch series: 2.0 mm)
6 ISO metric thread (fine pitch series: 3.0 mm)
7 ISO metric thread (fine pitch series: 4.0 mm)
8 Unified coarse thread (UNC): number sizes
9 Unified coarse thread (UNC): fractional inch sizes
10 Unified fine thread (UNF): number sizes
11 Unified fine thread (UNF): fractional inch sizes
12 British Standard parallel pipe thread (RP)
13 British Standard parallel pipe thread (G)
14 British Standard taper pipe thread (Rc)
15 British Standard Whitworth thread (BSW)
16 British Standard fine thread (BSF)
17 British Association thread (BA)
18 ISO metric thread (coarse pitch series): alternative
    sizes
19 ISO metric thread (fine pitch series: 0.25 mm, 0.35
    mm, 0.50 mm and 0.75 mm): alternative sizes
20 ISO metric thread (fine pitch series: 1.00 mm and
    1.25 mm): alternative sizes
21 ISO metric thread (fine pitch series: 1.5 mm):
    alternative sizes
22 ISO metric thread (fine pitch series: 2.0 mm):
    alternative sizes
23 ISO metric thread (fine pitch series: 3.0 mm):
    alternative sizes
24 Unified coarse thread (UNC): number sizes:
    alternative sizes
25 Unified coarse thread (UNC): fractional inch sizes:
    alternative sizes
26 Unified fine thread (UNF): number sizes:
    alternative sizes
27 Unified fine thread (UNF): fractional inch sizes:
    alternative sizes
28 British Standard parallel pipe thread (RP):
    alternative sizes
29 British Standard parallel thread (G): alternative
    sizes
30 British Standard Whitworth thread (BSW):
    alternative sizes
31 British Standard fine thread (BSF): alternative
    sizes
32 British Association thread (BA): alternative sizes
Figures
1 Whitworth and British Association (BA) thread forms
2 ISO metric and Unified thread forms

Sizes for ISO internal metric threads to BS 3643 (Parts 1, 2 and 3) and for internal threads to BS 21, 84, 93, 1580 (Parts 1, 2 and 3) and 2779. Alternative sizes in appendix.

These recommendations give drill sizes, covered by BS 328-1, for use prior to tapping the threads indicated. Table 1 to Table 14 cover preferred thread forms and Table 15 to Table 17 cover non-preferred forms. Appendix A covers alternative tapping drill sizes.