1/8" BSP tapered (R1/8 / BSPT): 9.728 mm major diameter, 28 thread, tapered, 55 degree. What it fits and the adapters to join it to other hose and tap threads.
Updated 05 September 2026.
1/8" BSP tapered (R1/8 / BSPT) (R1/8)
Where R1/8 is used, its real dimensions, and how to connect it to other standards.
Used on: small gauge and low-flow ports.
R1/8 is the tapered (BSPT / BS 21 / ISO 7) form of the G1/8 parallel thread, 9.728 mm major diameter at 28 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 1/8" BSP tapered (R1/8 / BSPT) (R1/8)?
R1/8
What is the major diameter of the 1/8" BSP tapered (R1/8 / BSPT) (R1/8)?
9.728 mm
What is the threads per inch / pitch of the 1/8" BSP tapered (R1/8 / BSPT) (R1/8)?
28
What is the thread form of the 1/8" BSP tapered (R1/8 / BSPT) (R1/8)?
tapered, 55 degree