NPT & NPSM Thread Identification

NPT – National Pipe Taper – ANSI/ASME B1.20.1-1983
NPSM – National Pipe Straight Mechanical – ANSI/ASME B1.20.1-1983

Dash Size	Thread Size – Threads Per Inch	NPT Male Thread Size		NPT Fixed Female Thread Size		NPSM Female Swivel Thread Size
usa	Size – TPI	mm	Inch	mm	Inch	mm	Inch
-2	1/8 – 27	9.89	0.39	8.41	0.33	8.59	0.34
-4	1/4 – 18	13.19	0.52	11.21	0.44	11.89	0.47
-6	3/8 – 18	16.61	0.65	14.69	0.58	14.99	0.59
-8	1/2 – 14	20.61	0.81	17.79	0.71	19.09	0.75
-12	3/4 – 14	26.01	1.02	23.39	0.92	24.59	0.97
-16	1 – 11.5	32.49	1.28	29.49	1.16	30.49	1.2
-20	1.1/4 – 11.5	41.21	1.62	38.09	1.5	39.39	1.55
-24	1.1/2 – 11.5	47.31	1.85	43.89	1.73	45.51	1.79
-32	2 – 11.5	59.29	2.32	56.39	2.22	57.41	2.26

* Thread size refers to the nominal bore of the pipe.
Subtract approx. 1/4″ (6mm) from thread diameter measurement for nominal pipe size.

NPT – NPT : NPT to fixed NPT female sealing is made through direct metal to metal contact. The use of Volz Thread Sealant is recommended.

NPT – NPSM : NPT male with conical 30° seat (60° included angle) seal against matching conical 30° seat of NPSM female swivel.