John Guest 5/16" push-fit (5/16" (8 mm) OD)
Where 5/16" (8 mm) OD is used, its real dimensions, and how to connect it to other keg fittings.
Published dimensions
- Designation
- 5/16" (8 mm) OD
- Size / thread
- 5/16" (about 7.94 mm)
- Fitting form
- push-fit collet, imperial
- Seals on
- single O-ring plus stainless collet grab-ring
- Rating / role
- John Guest Speedfit rated 16 bar at 1 C, 10 bar at 20 C
Used on: UK and US draft dispense, coolers and beer lines specified in inches.
John Guest 5/16 and Duotight 8mm are close enough that the O-ring seals across both, and brewers mix them in practice. The gap is real though: 5/16 inch is 7.94mm, so on long or high-pressure runs stay within one system.
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
Sources: John Guest Speedfit push-fit fitting technical data