British Standard Fine (BSF) tapping drill sizes.


Ø = diameter
" = inch
TPI = threads per inch

Tap Size TPI Tapping Drill
Ømm
Clearance drill
Ømm
3/16" 32 3.95 4.90
7/32" 28 4.63 5.70
1/4" 26 5.35 6.50
9/32" 26 6.10 7.4
5/16" 22 6.75 8.1
3/8" 20 8.22 9.70
7/16" 18 9.6 11.30
1/2" 16 11.1 13.0
9/16" 16 12.70 14.50
5/8" 14 14.00 16.25
11/16" 14 15.60 17.75
3/4" 12 16.9 19.25
7/8" 11 19.85 22.50
1" 10 22.75 25.75
1.1/8" 9 25.7 29.0
1.1/4" 9 28.80 32.0
1.3/8" 8 31.60 35.50
1.1/2" 8 34.80 38.50

BSF thread information.

BSF thread BS 84: 1956.
Developed by Joseph Whitworth in 1841 the thread has the same profile as the BSW thread, for use when a finer pitch was required.
The angle between the thread flanks is 55° and the thread has radii at both the roots and the crests of the thread.