Pipe thread chart (NPT / BSPT / BSPP)

30 sizes · ThreadRef · free sample of 8 representative sizes

Pipe thread chart (NPT / BSPT / BSPP). Tapered and parallel pipe threads on one sheet: trade size, form, threads per inch, major and pitch diameters, and the tap drill where the form has one.
Size	Form	TPI	Major dia mm	Major dia in	Pitch dia mm	Tap drill mm
NPT - American tapered pipe
1/8" NPT	NPT	27	10.29	0.4051	9.679	8.74
1/4" NPT	NPT	18	13.72	0.5402	12.803	11.11
1/2" NPT	NPT	14	21.34	0.8402	20.162	17.86
3/4" NPT	NPT	14	26.67	1.05	25.492	23.42
1" NPT	NPT	11.5	33.4	1.315	31.965	29.36
BSPT (R) - British tapered pipe
1/2" BSPT	BSPT	14	20.95	0.825	19.777	18.25
BSPP (G) - British parallel pipe
1/2" BSPP¹	BSPP	14	20.95	0.825	19.777	not defined
1" BSPP¹	BSPP	11	33.25	1.309	31.749	not defined

NPT per ASME B1.20.1; BSPT (R) per ISO 7-1 / BS 21; BSPP (G) per ISO 228-1. Trade sizes are nominal and are not the thread's measured diameter.

Torque figures are estimates that depend on the stated nut-factor assumption. Verify against your fastener manufacturer's data and joint requirements before assembly.

Every figure on this chart is also free on its own size page - tap any size in the first column to open it, or browse the full reference. Premium pays for the sheet, not the numbers.