US Patent 7381199 Structure of safety hypodermic syringe

A safety hypodermic syringe includes a barrel, which has a tapered hollow connector disposed at the front side and holds a needle assembly, a hollow plunger inserted into the barrel, and a retainer, which is fastened to the front side of the hollow plunger to keep the hollow plunger in a vacuum status and forced into engagement with the tapered hollow connector after the service of the safety hypodermic syringe for enabling the needle assembly and the retainer to be sucked into the inside of the hollow plunger after breaking of the tapered hollow connector from the barrel.