Tapping Chart: NPT National Pipe Taper Threads
NPT Size Tap Drill
(NTP/NPTF)
Tap Drill
(NPS)
Pipe OD Thread Length
1/16-27 D 1/4 0.313
1/8-27 R S 0.405 0.375
1/4-18 7/16 29/64 0.540 0.625
3/8-18 9/16 19/32 0.675 0.625
1/2-14 45/64 47/64 0.840 0.750
3/4-14 29/32 15/16 1.050 0.750
1-11-1/2 1-5/32 1-3/16 1.315 0.875

Taper angle: 1.79° (3/4" per foot)