TR21-4 soda cylinder valve (TR21x4 (soda / SodaStream-style))
Where TR21x4 (soda / SodaStream-style) is used, its real dimensions, and how to connect it to other keg fittings.
Published dimensions
- Designation
- TR21x4 (soda / SodaStream-style)
- Size / thread
- TR21 x 4 mm pitch trapezoidal
- Fitting form
- trapezoidal cylinder valve, external
- Seals on
- O-ring on the valve stem
- Rating / role
- small refillable soda-maker CO2 cylinders
Used on: SodaStream-compatible and small soda-maker CO2 cylinders that some brewers repurpose for kegging.
TR21-4 is a trapezoidal soda-cylinder thread, not a welding-gas standard, so it needs a TR21-4 to CGA-320 or W21.8 adapter to reach a normal keg regulator. Genuine SodaStream cylinders often use a proprietary valve on top of this and can need their own adapter.
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: CO2Art guide to cylinder connections (CGA320, W21.8, DIN477, BS341, G5/8, TR21-4)