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Fittings NPT versus BSPT Thread Sizing Charts

April 9, 2019

Fittings NPT versus BSPT Thread Sizing Charts

Fittings NPT versus BSP Thread Sizing Charts

BSP

BSP thread form stands for British Standard Pipe and is common in Australia and the commonwealth countries. It is based on trade size rather than actual diameter which can lead to some confusion when measuring ports.

There are two types of BSP threads;
- Parrallel (BSPP) - also known as G or Rp
- Tapered (BSPT) - also know as R or Rc

Both threads have the same pitch, angle (55 degrees) and shape (rounded peaks and valleys).

The below table gives the major and minor diameter for each BSP Trade Thread Size.

Trade Size	Threads per inch	Pitch		Major Diameter		Minor Diameter		Gage Length
Trade Size	Threads per inch	Inch	mm	Inch	mm	Inch	Mm	Inch	mm
1/8	28	0.0357	0.907	0.383	9.728	0.3372	8.565	0.1563	3.97
1/4	19	0.0526	1.337	0.518	13.157	0.4506	11.445	0.2367	6.012
3/8	19	0.0526	1.337	0.656	16.662	0.5886	14.95	0.25	6.35
1/2	14	0.0714	1.814	0.825	20.955	0.7336	18.633	0.3214	8.164
3/4	14	0.0714	1.814	1.041	26.441	0.9496	24.12	0.375	9.525
1	11	0.0909	2.309	1.309	33.249	1.1926	30.292	0.4091	10.391
1 ¼	11	0.0909	2.309	1.65	41.91	1.5336	38.953	0.5	12.7
1 ½	11	0.0909	2.309	1.882	47.803	1.7656	44.846	0.5	12.7
2	11	0.0909	2.309	2.347	59.614	2.2306	56.657	0.625	15.875
2 ½	11	0.0909	2.309	2.96	75.184	2.8436	72.227	0.6875	17.463
3	11	0.0909	2.309	3.46	87.884	3.3436	84.927	0.8125	20.638
4	11	0.0909	2.309	4.45	113.03	4.3336	110.073

NPT

NPT stands for National Pipe Thread and is an American standard thread. It may also be reffered to as MPT , MNPT or NPT (M) for male external threads and FPT, FNPT or NPT(F) for female interal threads. A thread sealant must always be used to achieve a leak free seal (except for NPTF). It is also based on Trade Size rather than actual diameter (similar to BSP in this regard).

Both threads have the same pitch, angle (60 degrees) and shape (flat peaks and valleys).

The below table gives the Threads Per Inch, Pithc and Major Diameter for NPT Threads.

Trade Size	Threads per inch	Pitch		Major Diameter (O.D)
Trade Size	Threads per inch	Inch	mm	Inch	mm
1/8	27	0.03704	0.94082	0.405	10.29
1/4	18	0.05556	1.41122	0.54	13.72
3/8	18	0.05556	1.41122	0.675	17.15
1/2	14	0.07143	1.81432	0.84	21.34
3/4	14	0.07143	1.81432	1.05	26.67
1	11 ½	0.08696	2.20878	1.315	33.4
1 ¼	11 ½	0.08696	2.20878	1.66	42.16
1 ½	11 ½	0.08696	2.20878	1.9	48.26
2	11 ½	0.08696	2.20878	2.375	60.33
2 ½	8	0.125	3.175	2.875	73.03
3	8	0.125	3.175	3.5	88.9
4	8	0.125	3.175	4.5	114.3