Not compatible. John Guest 12mm push-fit and John Guest 1/2" 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 12mm push-fit to John Guest 1/2" push-fit
How to join 12 mm OD and 1/2" (12.7 mm) OD, and what stops it leaking.
Not compatible. John Guest 12mm push-fit and John Guest 1/2" 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 12mm push-fit (12 mm OD)
- End B
- John Guest 1/2" push-fit (1/2" (12.7 mm) OD)
- A seals on
- single O-ring plus a stainless collet grab-ring
- B seals on
- single O-ring plus a stainless collet grab-ring
- Part needed
- matched replacement, no adapter exists
The part to buy
12mm John Guest is metric and 1/2 inch (12.7mm) is imperial, so despite looking the same size they do not interchange: a 1/2 tube will not seat in a 12mm collet or the reverse. Pick the collet for the tube standard, there is no adapter between them.
12mm versus 12.7mm is a small gap but a real one on a large-bore line under pressure. Read the tube spec, metric or imperial, and buy the matching John Guest size rather than trusting that a half-inch tube fits a 12mm fitting.
Related connections
Questions and answers
Connect John Guest 12mm push-fit to John Guest 1/2" push-fit?
Not compatible. John Guest 12mm push-fit and John Guest 1/2" push-fit do not share a mating thread, so there is no adapter between them; fit the part that matches your hardware.