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)