Connect 1/2" BSP parallel (G1/2 / BSPP) to 3/4" BSP parallel (G3/4 / BSPP)
How to join G1/2 and G3/4, and what stops it leaking.
Needs adapter
End A
1/2" BSP parallel (G1/2 / BSPP) (G1/2)
Seals on flat washer
via adapter
End B
3/4" BSP parallel (G3/4 / BSPP) (G3/4)
Seals on flat washer or bonded seal on the face
Adapter neededG1/2 to G3/4 tap thread adapter
Not a direct fit. Joining 1/2" BSP parallel (G1/2 / BSPP) to 3/4" BSP parallel (G3/4 / BSPP) needs a G1/2 to G3/4 tap thread adapter.
The adapter to buy
Search Amazon for G1/2 to G3/4 tap thread adapteraffiliate searchFind G1/2 to G3/4 tap thread adapter on eBayaffiliate
A 1/2 inch BSP indoor tap steps up to the 3/4 inch BSP a hose fitting expects with a short G1/2-to-G3/4 adapter. Both threads are parallel and seal on a washer, so this is a clean, reliable join.
Buy the version with a captive washer. A dry metal-to-metal step will weep under mains pressure.
Related connections
1/2" BSP parallel (G1/2 / BSPP)G1/23/4" BSP parallel (G3/4 / BSPP)G3/4Garden Hose Thread (GHT / NH) to 3/4" BSP parallel (G3/4 / BSPP)adapterGarden Hose Thread (GHT / NH) to 1/2" BSP parallel (G1/2 / BSPP)adapter3/8" BSP parallel (G3/8 / BSPP) to 1/2" BSP parallel (G1/2 / BSPP)adapter3/4" BSP parallel (G3/4 / BSPP) to 1" BSP parallel (G1 / BSPP)adapter
Sources: ISO 228-1 (G / BSPP parallel pipe threads) · BSP thread dimensions chart (ISO 228 / ISO 7), AmesWeb · Washing-machine / dishwasher inlet 3/4 BSP connector data