British Standard Fine (BSF) tapping drill sizes.

Nominal Dia Pitch Pitch TPI Tapping drill Dia mm
3/16" 32 4.00
7/32" 28 4.60
1/4" 26 5.30
9/32" 26 6.10
5/16" 22 6.80
3/8" 20 8.30
7/16" 18 9.70
1/2" 16 11.10
9/16" 16 12.70
5/8" 14 14.00
11/16" 14 15.50
3/4" 12 16.75
7/8" 11 19.75
1" 10 22.75
1.1/8" 9 25.50
1.1/4" 9 28.50
1.3/8" 8 31.50
1.1/2" 8 34.50