Not a direct fit. Joining 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" BSP tapered (R2-1/2 / BSPT) needs a G2-1/2 parallel to R2-1/2 tapered BSP adapter. Sealing method, the real-world trap, and the exact adapter to buy.
Updated 05 September 2026.
Connect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" BSP tapered (R2-1/2 / BSPT)
How to join G2-1/2 and R2-1/2, and what stops it leaking.
Not a direct fit. Joining 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" BSP tapered (R2-1/2 / BSPT) needs a G2-1/2 parallel to R2-1/2 tapered BSP adapter.
The adapter to buy
A parallel G2-1/2 (BSPP) female and a tapered R2-1/2 (BSPT) male are the same nominal BSP size and will start together, but they seal differently: the parallel end seals on a washer or bonded seal at the face, the tapered end seals on the thread flanks as it tightens. Use a dedicated parallel-to-taper adapter, or set the joint up so only one end does the sealing.
Mixing parallel and tapered BSP at 2-1/2 inch is a partial fit that often weeps. Decide which end makes the seal and prepare that end for it; do not rely on both the washer and the taper at once.
Related connections
Questions and answers
Connect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" BSP tapered (R2-1/2 / BSPT)?
Not a direct fit. Joining 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" BSP tapered (R2-1/2 / BSPT) needs a G2-1/2 parallel to R2-1/2 tapered BSP adapter.