Comparison
BSPP vs BSPT
Both are British-form 55° threads: BSPP (G) is parallel and seals on a cone seat, washer, or O-ring; BSPT (R) is tapered and seals on thread interference. Same family, different geometry — a parallel fitting in a tapered port seals on nothing.
Side by side
The decision table.
| BSPP | BSPT | |
|---|---|---|
| Geometry | Parallel (constant OD) | Tapered |
| Marking | G (e.g. G1/2) | R / PT (e.g. R1/2) |
| Seal | 60° cone, bonded washer, O-ring | Thread deformation |
| Sealant | Not on threads | Paste on threads |
| Typical use | Unions, swivels, ports w/ washer | Older ports, Asian equipment |
Choose BSPP when…
- Hose unions and component ports with a shoulder or spotface
Choose BSPT when…
- Legacy tapered ports marked R or PT
What happens if you mix them
G into R (or vice versa) engages a few threads and feels 'almost right.' Under pressure it weeps at the interface. Check whether the thread tapers before anything else.
BSPP vs BSPT — FAQs
How can I tell G from R with calipers?
Measure OD at the first and sixth thread: equal = parallel (G); shrinking = taper (R).
Do BSPP ports need a special washer?
Port connections usually seal with a bonded (Dowty) washer or O-ring under the shoulder — we stock both in all common sizes.
Still deciding?
Bring both fittings to the counter — or call (817) 589-7101 and read us the layline. We settle these in minutes, with the gauges out.