4" BSP tapered (R4 / BSPT): 113.03 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.
4" BSP tapered (R4 / BSPT) (R4)
Where R4 is used, its real dimensions, and how to connect it to other standards.
Used on: very large transfer, tank and industrial water pipework.
R4 is the tapered (BSPT / BS 21 / ISO 7) form of the G4 parallel thread, 113.03 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.
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Questions and answers
What is the designation of the 4" BSP tapered (R4 / BSPT) (R4)?
R4
What is the major diameter of the 4" BSP tapered (R4 / BSPT) (R4)?
113.03 mm
What is the threads per inch / pitch of the 4" BSP tapered (R4 / BSPT) (R4)?
11
What is the thread form of the 4" BSP tapered (R4 / BSPT) (R4)?
tapered, 55 degree