Connecting Threads

BSP (British Standard Pipe)
		PARALLEL	APPROX. TAPER
Nominal Size	TPI (Threads per Inch)	Actual O.D.	Min. Diameter	Max. Diameter
1/8''	28	0.377	0.337	0.406
1/4''	19	0.511	0.451	0.531
3/8''	19	0.648	0.598	0.687
1/2''	14	0.814	0.734	0.843
3/4''	14	1.03	0.95	1.062
1''	11	1.295	1.193	1.343

NPS/NPT (National Pipe Straight)/(National Pipe Taper)
		PARALLEL	APPROX. TAPER
Nominal Size	TPI (Threads per Inch)	Actual O.D.	Min. Diameter	Max. Diameter
1/8''	27	0.405	0.393	0.405
1/4''	18	0.54	0.522	0.54
3/8''	18	0.675	0.656	0.675
1/2''	14	0.84	0.816	0.84
3/4''	14	1.05	1.025	1.05
1''	11.5	1.315	1.283	1.315

UNF (Unified National Fine)
			PARALLEL
Nominal Size	TPI (Threads per Inch)	Major Diameter	Actual O.D.
1/8''	28	5/16-24	0.312
3/16''	18	3/8-24	0.375
1/4''	19	7/16-20	0.437
5/16''	18	1/2-20	0.5
3/8''	19	9/16-18	0.562
1/2''	14	3/4-16	0.75
3/4''	14	1-1/16''-14	1.062