2-1/2" BSP parallel (G2-1/2 / BSPP): 75.184 mm major diameter, 11 thread, parallel, 55 degree. What it fits and the adapters to join it to other hose and tap threads.

Updated 05 September 2026.

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2-1/2" BSP parallel (G2-1/2 / BSPP) (G2-1/2)

Where G2-1/2 is used, its real dimensions, and how to connect it to other standards.

G2-1/2Thread standard
DesignationG2-1/2
Major diameter75.184 mm
Threads per inch / pitch11
Thread formparallel, 55 degree
Seals onflat washer or bonded seal on the face

Used on: large pumps, tank outlets and industrial water lines.

G2-1/2 is a BSP parallel thread of 75.184 mm major diameter at 11 TPI, cut to the 55 degree Whitworth form of ISO 228. Being parallel it seals on a washer or bonded seal at the face, not on the thread flanks.

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

Connect to 1-1/2 inch camlock couplingneeds an adapterConnect to 2" camlock (cam-and-groove) couplingneeds an adapterConnect to 3 inch camlock couplingneeds an adapterConnect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" BSP tapered (R2-1/2 / BSPT)needs an adapterConnect 2-1/2" NPT (National Pipe Taper) to 2-1/2" BSP parallel (G2-1/2 / BSPP)needs an adapterConnect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" NPSH straight hose threadneeds an adapterConnect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2-1/2" NH fire hose thread (NST)needs an adapterConnect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 1-1/4" BSP parallel (G1-1/4 / BSPP)needs an adapterConnect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 1-1/2" BSP parallel (G1-1/2 / BSPP)needs an adapterConnect 2-1/2" BSP parallel (G2-1/2 / BSPP) to 2" BSP parallel (G2 / BSPP)needs an adapter

Questions and answers

What is the designation of the 2-1/2" BSP parallel (G2-1/2 / BSPP) (G2-1/2)?

G2-1/2

What is the major diameter of the 2-1/2" BSP parallel (G2-1/2 / BSPP) (G2-1/2)?

75.184 mm

What is the threads per inch / pitch of the 2-1/2" BSP parallel (G2-1/2 / BSPP) (G2-1/2)?

11

What is the thread form of the 2-1/2" BSP parallel (G2-1/2 / BSPP) (G2-1/2)?

parallel, 55 degree