This adapter kit is used to fill Sodastream cylinders with Tr21-4 thread from a large CO2 tank with W21.8-14 thread. With pressure gauge 2000 psi, vent valve, quick coupler 8 mm Input: W21.8-14 thread (gold connector) Filling: Tr21-4 thread (black adapter) Material: Brass and Aluminum How does it work? Please put a small cylinder in the refrigerator to cool it down and be sure that it can be refilled with more carbon dioxide. Check that the on/off valve (at a 90-degree angle to the ball valve body) and the vent valve are closed, then turn the knob (orange cap) upwards (counterclockwise). Place the white gasket in the gold connector, then connect it to a large CO2 tank (tighten with a wrench). Connect the small sodastream cylinder to the black adapter. Turn the pin knob down to lightly touch the cylinder pin (clockwise). (If you press the pin too hard, the gaz will be stopped by the check valve when filling the cylinder with a 6 mm wide pin.) Open the valve of the large CO2 tank. Slowly open the on/off valve (counterclockwise) and close it after 2-3 seconds, then open the vent valve to release the remaining gaz in a small cylinder. Finally, remember to close the vent valve. Carefully open the on/off valve (20 to 30 degrees counterclockwise) to carry out the charging process for 30 to 60 seconds, then close the large carbon dioxide tank valve (make sure the on/off valve is open). After filling, set the knob in the highest position and open the vent valve to release the remaining gaz in this object. After inflation, unscrew the small cylinder. Repeat the filling process for each cylinder.-Ready. *Pack contains only 1 piece of adapter set, excluding tanks