Tr21 vs W218: specs compared
Updated 05 September 2026.
5
specs differ
Tr21 and W218 differ on 5 specs: designation, size / thread, fitting form, seals on, rating / role.
| Spec | Tr21 | W218 |
|---|---|---|
| Designation | TR21x4 (soda / SodaStream-style) | W21.8-14 (DIN 477 / BS 341 No.8) |
| Size / thread | TR21 x 4 mm pitch trapezoidal | W21.8 x 1/14" (22 mm, 14 TPI) |
| Fitting form | trapezoidal cylinder valve, external | cylinder valve outlet nut, external |
| Seals on | O-ring on the valve stem | captive O-ring or washer in the nut against the valve outlet |
| Rating / role | small refillable soda-maker CO2 cylinders | the European, UK, Oceania and Asian CO2 cylinder connection |
Questions and answers
How do Tr21 and W218 compare?
Tr21 and W218 differ on 5 specs: designation, size / thread, fitting form, seals on, rating / role.