G5/8 regulator inlet (G5/8 (BSP parallel))

Where G5/8 (BSP parallel) is used, its real dimensions, and how to connect it to other keg fittings.

Published dimensions

Designation: G5/8 (BSP parallel)
Size / thread: G5/8 (5/8" BSP parallel)
Fitting form: parallel pipe thread, regulator side
Seals on: flat washer on the face of the inlet
Rating / role: a common regulator inlet thread that a CGA-320 or W21.8 adapter presents

Used on: the inlet body of some CO2 regulators, fed by a CGA-320 or W21.8 to G5/8 adapter.

G5/8 is on the regulator, not the cylinder. Cylinder-connection adapters are sold as CGA-320, W21.8 or G5/8 male to match whatever your regulator inlet is, which is why the cylinder standard and the regulator inlet are two separate things to check.

Flare fittings seal on the 45 degree flare face and must never be taped. Push-in fittings seal on an O-ring against the tube wall and need the tube cut square. Barbs seal under a worm clamp. Getting the sealing method right matters more than the thread label, because most homebrew leaks are a taped flare or an unclamped barb.

Connect this fitting

Connect CGA-320 CO2 cylinder valve to G5/8 regulator inletneeds an adapter Connect W21.8 CO2 cylinder valve to G5/8 regulator inletneeds an adapter CGA-320 CO2 cylinder valverelated fitting (0.825"-14 NGO RH)W21.8 CO2 cylinder valverelated fitting (W21.8-14 (DIN 477 / BS 341 No.8))TR21-4 soda cylinder valverelated fitting (TR21x4 (soda / SodaStream-style))CGA-580 nitrogen / beer-gas cylinder valverelated fitting (0.965"-14 NGO RH)SodaStream CO2 cylinderrelated fitting (TR21-4 (often pin-valve))

Sources: CO2Art guide to cylinder connections (CGA320, W21.8, DIN477, BS341, G5/8, TR21-4) · ISO 228-1 (G / BSP parallel pipe threads)