Unifed National Coarse (UNC) tapping drill sizes.

Nominal Dia Pitch Pitch TPI Tapping drill Dia mm
No. 1 64 1.55
No. 2 56 1.85
No. 3 48 2.10
No. 4 40 2.35
No. 5 40 2.65
No. 6 32 2.85
No. 8 32 3.50
No. 10 24 3.90
No. 12 24 4.50
1/4" 20 5.10
5/16" 18 6.60
3/8" 16 8.00
7/16" 14 9.40
1/2" 13 10.80
9/16" 12 12.20
5/8" 11 13.50
3/4" 10 16.50
7/8" 9 19.50
1" 8 22.25
1.1/8" 7 25.00
1.1/4" 7 28.00
1.3/8" 6 30.75
1.1/2" 6 34.00
1.3/4" 5 39.50
2" 4.5 45.00