John Guest 4mm push-fit: 4 mm OD tube, push-fit collet, metric, seals on single O-ring plus a stainless collet grab-ring. What it fits and the adapters to join it to other keg fittings.
Updated 05 September 2026.
John Guest 4mm push-fit (4 mm OD)
Where 4 mm OD is used, its real dimensions, and how to connect it to other keg fittings.
Published dimensions
- Designation
- 4 mm OD
- Size / thread
- 4 mm OD tube
- Fitting form
- push-fit collet, metric
- Seals on
- single O-ring plus a stainless collet grab-ring
- Rating / role
- John Guest Speedfit metric fittings for 4mm OD tube; tube OD must be within 0.1mm of nominal
- Tube OD
- 4 mm
Used on: very small gas jumpers and sample lines in the John Guest metric range.
4mm is the smallest John Guest metric size and does not interchange with any imperial tube. A 4mm collet grips only 4mm OD tube, so a 5/16 or 6mm tube will not seat in it. Match the fitting size to the printed tube OD, not to a nominal inch label.
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
Questions and answers
What is the designation of the John Guest 4mm push-fit (4 mm OD)?
4 mm OD
What is the size / thread of the John Guest 4mm push-fit (4 mm OD)?
4 mm OD tube
What is the fitting form of the John Guest 4mm push-fit (4 mm OD)?
push-fit collet, metric
What is the seals on of the John Guest 4mm push-fit (4 mm OD)?
single O-ring plus a stainless collet grab-ring