The Valken Propane Tank Fill Adapter allows you to fill your GBB magazines and airsoft grenades with affordable, widely available propane that is easily found in many big box stores. The propane adapter is constructed of a strong aluminum alloy, so it is one of the strongest adapters available. We recommend placing 2 drops of silicone oil in your GBB magazine fill valve before filling with propane so the rubber seals do not dry out and crack. Reapply silicone oil about every 6-8 fills