Medi-Vac® Brand Guardian™ Direct-To-Regulator Canister System - Our direct-to-regulator canister system eliminates the need for a ring bracket and additional tubing. It mounts directly to the regulator; raised ribs on the connection help make attachment easy. This disposable hard canister system requires no liner and has a 1200cc capacity. Male diameter index safety system (DISS) available separately. 36 canister systems per case.