2-1/2" BSP tapered (R2-1/2 / BSPT): 75.184 mm major diameter, 11 thread, tapered, 55 degree. What it fits and the adapters to join it to other hose and tap threads.
Updated 05 September 2026.
2-1/2" BSP tapered (R2-1/2 / BSPT) (R2-1/2)
Where R2-1/2 is used, its real dimensions, and how to connect it to other standards.
Used on: large pumps, tank outlets and industrial water lines.
R2-1/2 is the tapered (BSPT / BS 21 / ISO 7) form of the G2-1/2 parallel thread, 75.184 mm major diameter at 11 TPI. It seals on the thread flanks as it tightens, so it is used with PTFE tape or paste, not a face washer.
Quick-connect click fittings from Hozelock, Gardena and Karcher are proprietary and do not interchange. They all sit on top of a standard thread underneath, so the reliable way to move between brands is to adapt at the threaded tap or hose-end fitting, then use each brand's own connector above it.
Connect this thread
Questions and answers
What is the designation of the 2-1/2" BSP tapered (R2-1/2 / BSPT) (R2-1/2)?
R2-1/2
What is the major diameter of the 2-1/2" BSP tapered (R2-1/2 / BSPT) (R2-1/2)?
75.184 mm
What is the threads per inch / pitch of the 2-1/2" BSP tapered (R2-1/2 / BSPT) (R2-1/2)?
11
What is the thread form of the 2-1/2" BSP tapered (R2-1/2 / BSPT) (R2-1/2)?
tapered, 55 degree