JIS Pipe Threads — PT, PF, R, Rc, Rp and G
What the Japanese designations mean, and which ISO thread each one is.
Designation map
| JIS mark | Old JIS mark | Standard | Same as | Form |
|---|---|---|---|---|
| R | PT | JIS B 0203 | BSPT (ISO 7-1) | Taper male |
| Rc | PT | JIS B 0203 | BSPT (ISO 7-1) | Taper female |
| Rp | PS | JIS B 0203 | ISO 7-1 Rp | Parallel female for a taper male |
| G | PF | JIS B 0202 | BSPP (ISO 228-1) | Parallel, male or female |
Japan renamed these designations to align with ISO. PT became R and Rc, PF became G, and PS became Rp. Older drawings, older catalogues and a great deal of machinery still in service use the PT and PF marks, so both sets are worth recognising.
The one thing that is genuinely different
JIS 30° flare fittings are not a thread standard and are frequently confused with these. A JIS 30° flare uses a BSPP (G) thread with a 30° cone seat machined into the fitting — the thread holds it together and the cone does the sealing. If you have a fitting with a G thread and a shallow internal cone, that is what you are looking at, and it will not seal against a flat-face BSPP fitting even though the threads mate perfectly.
So can you mix JIS and BSP parts?
R against Rc, and R against Rp: yes. These are the same threads as their ISO 7-1 equivalents and interchange freely with BSPT parts.
G against G: yes on the thread — but check the sealing arrangement, because a JIS 30° flare and a plain BSPP port both carry a G thread and seal completely differently.
Anything against NPT: no. NPT is 60° and all of these are 55°. See NPT vs BSP.