Connect 3/4" BSP parallel (G3/4 / BSPP) to 1" BSP parallel (G1 / BSPP)
How to join G3/4 and G1, and what stops it leaking.
Needs adapter
End A
3/4" BSP parallel (G3/4 / BSPP) (G3/4)
Seals on flat washer or bonded seal on the face
via adapter
End B
1" BSP parallel (G1 / BSPP) (G1)
Seals on flat washer or bonded seal on the face
Adapter neededG3/4 to G1 BSP adapter
Not a direct fit. Joining 3/4" BSP parallel (G3/4 / BSPP) to 1" BSP parallel (G1 / BSPP) needs a G3/4 to G1 BSP adapter.
The adapter to buy
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Stepping a 3/4 inch BSP fitting up to a 1 inch BSP port uses a parallel G3/4-to-G1 adapter. Both are BSP parallel and seal on a washer or bonded seal, so the mismatch is only in size, not thread form.
A 1 inch fitting is not always G1. Check it is not 1 inch NPT or NH first, because those need a different adapter entirely.
Related connections
3/4" BSP parallel (G3/4 / BSPP)G3/41" BSP parallel (G1 / BSPP)G1Garden Hose Thread (GHT / NH) to 3/4" BSP parallel (G3/4 / BSPP)adapter1/2" BSP parallel (G1/2 / BSPP) to 3/4" BSP parallel (G3/4 / BSPP)adapterMale aerator thread (M22 x 1 / 15/16"-27) to 3/4" BSP parallel (G3/4 / BSPP)adapterM22 x 1.5 pressure-washer, 15 mm bore to 3/4" BSP parallel (G3/4 / 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