R2-1/2 vs 2-1/2-8 NPT: specs compared

Updated 05 September 2026.

75.184 mm
R2-1/2 wins on major diameter

On major diameter, R2-1/2 leads: 75.184 mm versus 73.02 mm.

SpecR2-1/22-1/2-8 NPT
DesignationR2-1/22-1/2-8 NPT
Major diameter75.184 mm73.02 mm
Threads per inch / pitch118
Thread formtapered, 55 degreetapered, 60 degree
Seals onon the thread flanks with PTFE tape or pasteon the thread flanks with PTFE tape

Questions and answers

Which has the higher major diameter, R2-1/2 or 2-1/2-8 NPT?

On major diameter, R2-1/2 leads: 75.184 mm versus 73.02 mm.

How do R2-1/2 and 2-1/2-8 NPT compare?

On major diameter, R2-1/2 leads: 75.184 mm versus 73.02 mm.

Compared here

2-1/2" BSP tapered (R2-1/2 / BSPT) (R2-1/2)2-1/2" NPT (National Pipe Taper) (2-1/2-8 NPT)