3/8-18 NPT vs 4-1/2-4NH: specs compared
Updated 05 September 2026.
146.3 mm
4-1/2-4NH wins on major diameter
On major diameter, 4-1/2-4NH leads: 146.3 mm versus 17.15 mm.
| Spec | 3/8-18 NPT | 4-1/2-4NH |
|---|---|---|
| Designation | 3/8-18 NPT | 4-1/2-4NH |
| Major diameter | 17.15 mm | 146.3 mm |
| Threads per inch / pitch | 18 | 4 |
| Thread form | tapered, 60 degree | straight (parallel), 60 degree |
| Seals on | on the thread flanks with PTFE tape | rubber gasket in the female swivel |
Questions and answers
Which has the higher major diameter, 3/8-18 NPT or 4-1/2-4NH?
On major diameter, 4-1/2-4NH leads: 146.3 mm versus 17.15 mm.
How do 3/8-18 NPT and 4-1/2-4NH compare?
On major diameter, 4-1/2-4NH leads: 146.3 mm versus 17.15 mm.