Reference

Thread Standards Reference

Metric (ISO), BSP (ISO 228), and NPT (ANSI/ASME B1.20.1) thread dimensions. Outer diameter, pitch, TPI, and typical use.

Metric threads

Size	OD (mm)	OD (inch)	Pitch (mm)	TPI	Typical use
M3	3.00	0.118	0.5	50.8	Electronics, small fasteners
M4	4.00	0.157	0.7	36.3	Electronics, light assemblies
M5	5.00	0.197	0.8	31.8	Machine screws, brackets
M6	6.00	0.236	1.0	25.4	General engineering
M8	8.00	0.315	1.25	20.3	Structural, automotive
M10	10.00	0.394	1.5	16.9	Structural bolts
M12	12.00	0.472	1.75	14.5	Heavy structural
M16	16.00	0.630	2.0	12.7	Heavy machinery, flanges
M20	20.00	0.787	2.5	10.2	Heavy industrial, anchors

Size	OD (mm)	OD (inch)	Pitch (mm)	TPI	Typical use
G 1/8"	9.73	0.383	0.907	28	Pneumatics, small fittings
G 1/4"	13.16	0.518	1.337	19	Pneumatics, hydraulics
G 3/8"	16.66	0.656	1.337	19	Plumbing, pneumatics
G 1/2"	20.96	0.825	1.814	14	Plumbing, pipe fittings
G 3/4"	26.44	1.041	1.814	14	Plumbing, water supply
G 1"	33.25	1.309	2.309	11	Plumbing, process piping

Size	OD (mm)	OD (inch)	Pitch (mm)	TPI	Typical use
1/8" NPT	10.29	0.405	0.941	27	Instrumentation, small fittings
1/4" NPT	13.72	0.540	1.411	18	Pneumatics, US plumbing
3/8" NPT	17.15	0.675	1.411	18	Gas lines, pneumatics
1/2" NPT	21.34	0.840	1.814	14	US plumbing, pipe fittings
3/4" NPT	26.67	1.050	1.814	14	US plumbing, water supply
1" NPT	33.40	1.315	2.209	11.5	US plumbing, process piping

BSP = British Standard Pipe (parallel/G-type shown). NPT = National Pipe Thread (tapered). OD values are nominal outside diameter of the male thread.

FacetFlux normalizes thread designations and cross-references between Metric, BSP, and NPT during enrichment.