Not compatible. John Guest 6mm push-fit and John Guest 5/16" push-fit do not share a mating thread, so there is no adapter between them; fit the part that matches your hardware. Sealing method, the real-world trap, and the exact part to buy.
Updated 05 September 2026.
Connect John Guest 6mm push-fit to John Guest 5/16" push-fit
How to join 6 mm OD and 5/16" (8 mm) OD, and what stops it leaking.
Not compatible. John Guest 6mm push-fit and John Guest 5/16" push-fit do not share a mating thread, so there is no adapter between them; fit the part that matches your hardware.
The two ends
- End A
- John Guest 6mm push-fit (6 mm OD)
- End B
- John Guest 5/16" push-fit (5/16" (8 mm) OD)
- A seals on
- single O-ring plus a stainless collet grab-ring
- B seals on
- single O-ring plus stainless collet grab-ring
- Part needed
- matched replacement, no adapter exists
The part to buy
6mm John Guest is metric and 5/16 (7.94mm) John Guest is imperial, so a 6mm tube will not seal in a 5/16 collet or the reverse. The two ranges are specified separately; there is no reducer that turns a metric collet into an imperial one, you fit the collet that matches the tube.
6mm and 5/16 look almost identical in a listing but differ by 1.9mm, enough to leak. Read whether your tube is metric (mm) or imperial (fractional) and buy the matching John Guest range rather than assuming they cross over.
Related connections
Questions and answers
Connect John Guest 6mm push-fit to John Guest 5/16" push-fit?
Not compatible. John Guest 6mm push-fit and John Guest 5/16" push-fit do not share a mating thread, so there is no adapter between them; fit the part that matches your hardware.