G1/4 vs 1/4-18 NPT: specs compared
Updated 05 September 2026.
13.72 mm
1/4-18 NPT wins on major diameter
On major diameter, 1/4-18 NPT leads: 13.72 mm versus 13.157 mm.
| Spec | G1/4 | 1/4-18 NPT |
|---|---|---|
| Designation | G1/4 | 1/4-18 NPT |
| Major diameter | 13.157 mm | 13.72 mm |
| Threads per inch / pitch | 19 | 18 |
| Thread form | parallel, 55 degree | tapered, 60 degree |
| Seals on | flat washer or bonded seal on the face | on the thread flanks with PTFE tape |
Questions and answers
Which has the higher major diameter, G1/4 or 1/4-18 NPT?
On major diameter, 1/4-18 NPT leads: 13.72 mm versus 13.157 mm.
How do G1/4 and 1/4-18 NPT compare?
On major diameter, 1/4-18 NPT leads: 13.72 mm versus 13.157 mm.