NPT		NPTF (Dryseal)		NPS (Straight)		NPSF (Dryseal)
Designation	Pipe size O.D.	TPI	Tap drill size	Decimal tap drill size	Tap drill size	Decimal tap drill size	Tap drill size	Decimal tap drill size	Tap drill size	Decimal tap drill size
1/16 - 27	.3125	27	D	0.2460	D	0.2460	1/4	0.2500	1/4	0.250
1/8 - 27	405	27	Q	0.3320	R	0.3390	11/32	0.3438	Q	0.332
1/4 - 18	.540	18	7/16	0.4375	7/16	0.4375	7/16	0.4375	7/16	0.438
3/8 - 18	.675	18	9/16	0.5625	37/64	0.5781	37/64	0.5781	37/64	0.578
1/2 - 14	.840	14	45/64	0.7031	45/64	0.7031	23/32	0.7188	45/64	0.703
3/4 - 14	1.05	14	29/32	0.7813	59/64	0.9219	59/64	0.9219	59/64	0.922
1 - 11 1/2	1.315	11.5	1 9/64	1.1406	1 5/32	1.1563	1 5/32	1.1563	1 5/32	1.156
1 1/4 - 11 1/2	1.660	11.5	1 31/64	1.4844	1 1/2	1.5000	1 33/64	1.5156
1 1/2 - 11 1/2	1.9	11.5	1 47/64	1.7344	1 47/64	1.7344	1 3/4	1.7500
2 - 11 1/2	2.375	11.5	2 13/64	2.2031	2 7/32	2.2188	2 7/32	2.2188

Last Updated: 20 February 2015