4-1/2-4NH vs 6-8 NPT: specs compared
Updated 05 September 2026.
168.27 mm
6-8 NPT wins on major diameter
On major diameter, 6-8 NPT leads: 168.27 mm versus 146.3 mm.
| Spec | 4-1/2-4NH | 6-8 NPT |
|---|---|---|
| Designation | 4-1/2-4NH | 6-8 NPT |
| Major diameter | 146.3 mm | 168.27 mm |
| Threads per inch / pitch | 4 | 8 |
| Thread form | straight (parallel), 60 degree | tapered, 60 degree |
| Seals on | rubber gasket in the female swivel | on the thread flanks with PTFE tape |
Questions and answers
Which has the higher major diameter, 4-1/2-4NH or 6-8 NPT?
On major diameter, 6-8 NPT leads: 168.27 mm versus 146.3 mm.
How do 4-1/2-4NH and 6-8 NPT compare?
On major diameter, 6-8 NPT leads: 168.27 mm versus 146.3 mm.