3-1/2-8 NPT vs G3/8: specs compared
Updated 05 September 2026.
101.6 mm
3-1/2-8 NPT wins on major diameter
On major diameter, 3-1/2-8 NPT leads: 101.6 mm versus 16.662 mm.
| Spec | 3-1/2-8 NPT | G3/8 |
|---|---|---|
| Designation | 3-1/2-8 NPT | G3/8 |
| Major diameter | 101.6 mm | 16.662 mm |
| Threads per inch / pitch | 8 | 19 |
| Thread form | tapered, 60 degree | parallel, 55 degree |
| Seals on | on the thread flanks with PTFE tape | flat washer or bonded seal on the face |
Questions and answers
Which has the higher major diameter, 3-1/2-8 NPT or G3/8?
On major diameter, 3-1/2-8 NPT leads: 101.6 mm versus 16.662 mm.
How do 3-1/2-8 NPT and G3/8 compare?
On major diameter, 3-1/2-8 NPT leads: 101.6 mm versus 16.662 mm.