This device allows the use of 12g CO2 cartridges in any marker with a standard ASA tank thread. Nothing complicated about using it. You just attach the front piece to the standard ASA, slip a 12-gram CO2 cartridge in the rear tube, and tighten. The cartridge is pierced and the CO2 flows into the marker.
Not to be confused with the 12g to 88 gram adaptor found HERE