1/4-18 NPT vs 1/8-27 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 10.29 mm.
| Spec | 1/4-18 NPT | 1/8-27 NPT |
|---|---|---|
| Designation | 1/4-18 NPT | 1/8-27 NPT |
| Major diameter | 13.72 mm | 10.29 mm |
| Threads per inch / pitch | 18 | 27 |
| Thread form | tapered, 60 degree | tapered, 60 degree |
| Seals on | on the thread flanks with PTFE tape | on the thread flanks with PTFE tape |
Questions and answers
Which has the higher major diameter, 1/4-18 NPT or 1/8-27 NPT?
On major diameter, 1/4-18 NPT leads: 13.72 mm versus 10.29 mm.
How do 1/4-18 NPT and 1/8-27 NPT compare?
On major diameter, 1/4-18 NPT leads: 13.72 mm versus 10.29 mm.