3/8-18 NPT vs R4: specs compared
Updated 05 September 2026.
113.03 mm
R4 wins on major diameter
On major diameter, R4 leads: 113.03 mm versus 17.15 mm.
| Spec | 3/8-18 NPT | R4 |
|---|---|---|
| Designation | 3/8-18 NPT | R4 |
| Major diameter | 17.15 mm | 113.03 mm |
| Threads per inch / pitch | 18 | 11 |
| Thread form | tapered, 60 degree | tapered, 55 degree |
| Seals on | on the thread flanks with PTFE tape | on the thread flanks with PTFE tape or paste |
Questions and answers
Which has the higher major diameter, 3/8-18 NPT or R4?
On major diameter, R4 leads: 113.03 mm versus 17.15 mm.
How do 3/8-18 NPT and R4 compare?
On major diameter, R4 leads: 113.03 mm versus 17.15 mm.