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Pipe Threads
NPT, BSPT and BSPP — 49 sizes, with the identification guides for telling them apart.
Pipe threads are named by nominal bore, not by any dimension
you can measure. A 1/2″ pipe thread is nowhere near 1/2″ across. If
you have measured a fitting and the number does not match anything, that is why —
find your measurement in the charts below rather than trusting the label.
Which thread am I holding?
Flat crests, 60°
NPT
Rounded crests, 55°, tapered
BSPT
Rounded crests, 55°, parallel
BSPP
Charts
NPT sizes
ASME B1.20.1. Tapered 1 in 16, 60° thread angle, seals on the thread.
BSPT sizes (R / Rc)
ISO 7-1 and BS 21. Tapered 1 in 16, 55° Whitworth form, seals on the thread.
BSPP sizes (G)
ISO 228-1. Parallel, 55° Whitworth form. Does not seal on the thread — needs a bonded washer, an O-ring or a cone seat.
G 1/16 G 1/8 G 1/4 G 3/8 G 1/2 G 5/8 G 3/4 G 7/8 G 1 G 1-1/8 G 1-1/4 G 1-1/2 G 1-3/4 G 2 G 2-1/4 G 2-1/2 G 2-3/4 G 3 G 3-1/2 G 4 G 4-1/2 G 5 G 5-1/2 G 6
NPT against BSPT, size by size
Whether a given size will screw together, whether it will seal, and how to tell which one you have before you find out the hard way.