Not compatible. John Guest 10mm push-fit and John Guest 3/8" 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 10mm push-fit to John Guest 3/8" push-fit
How to join 10 mm OD and 3/8" (9.5 mm) OD, and what stops it leaking.
Not compatible. John Guest 10mm push-fit and John Guest 3/8" 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 10mm push-fit (10 mm OD)
- End B
- John Guest 3/8" push-fit (3/8" (9.5 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
10mm John Guest is metric and 3/8 (9.53mm) is imperial, so a 3/8 tube will not seat reliably in a 10mm collet. They are close in size but specified separately, and there is no adapter between two collets, only the correct collet for the tube you run.
The 0.47mm gap between 10mm and 3/8 is enough to weep on a long warm beer run. Confirm the tube is metric or imperial before buying, and keep one run in one standard rather than mixing 10mm and 3/8 fittings.
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Questions and answers
Connect John Guest 10mm push-fit to John Guest 3/8" push-fit?
Not compatible. John Guest 10mm push-fit and John Guest 3/8" push-fit do not share a mating thread, so there is no adapter between them; fit the part that matches your hardware.