SodaStream CO2 cylinder (TR21-4 (often pin-valve))
Where TR21-4 (often pin-valve) is used, its real dimensions, and how to connect it to other keg fittings.
Published dimensions
- Designation
- TR21-4 (often pin-valve)
- Size / thread
- TR21 x 4 mm trapezoidal, frequently behind a proprietary quick-connect valve
- Fitting form
- soda-maker CO2 cylinder
- Seals on
- O-ring on the valve stem
- Rating / role
- small refillable soda cylinder brewers repurpose for kegging
Used on: carbonating and low-volume kegging off a cheap soda cylinder instead of a full CO2 tank.
A SodaStream cylinder threads TR21-4 underneath, but newer bottles hide it behind a proprietary quick-connect valve, so a plain TR21-4 adapter may not fit. A deluxe SodaStream to CGA-320 adapter with pin adjustment (KegLand KL24662) reaches both styles and presents a CGA-320 nut for a normal keg regulator.
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: MoreWinePro / KegLand deluxe SodaStream cylinder adapter (CGA320 male x TR21-4 female, pin adjustment KL24662) ยท CO2Art guide to cylinder connections: disposable/small cylinder threads (M10x1, 3/8-24 UNF 16g, 5/8-24 UNF 74g, M16x1.5 95g)