A plastic top for adapting to a chosen syringe (14) a standard cartridge (8) of the kind having a neck (9) with a flange (10) and being closed by a rubber membrane (11) sealingly secured against the flange (10) by a metal cover (12) having its edge beaded behind the flange. This plastic top has a bore (2) for receiving the neck part (9) of the cartridge (8), which bore (2) has a diameter making it fit over the metal cover (12) and is provided with protrusions (3;9) gripping behind the edge of the metal cover (12) when the neck part (9) is inserted in the bore. The outer contour of the plastic top is adapted to the syringe type in which the cartridge is going to be used. The plastic top is provided with a thread (5;18) coaxial with the bore to receive a needle hub (13) in a way making its needle (15) penetrate the membrane (11) of the cartridge (8) when the hub (13) is mounted on the thread (5) of the plastic top.