Patent ID: 7371226

Claim:
A plunger of a syringe, contained in a needle barrel of a syringe, comprising: a hook unit having a central rod and a push wing extended backward from a lateral wall of said central rod, whereby said push wing will be flexibly attached onto said central rod when said hook unit is driven into a receptacle formed at a base of said needle at a front end of said needle barrel, and whereby said needle will be drawn into said needle barrel when said plunger is pulled backward; and wherein, as said push wing is relaxed with respect to said central rod, a radius defined by the minimal distance between an axis of said central rod and an outmost edge of said push wing is slightly larger than a radius defined by the minimal distance between the center of an entrance hole of said receptacle and an outmost boundary of a terminal cavity of said receptacle; and wherein said push wing will be attached onto said central rod to form a hook unit by a lateral pressure force, whereby the largest radius thereof will be larger than the inner radius of said entrance hole of said receptacle; and wherein said central rod has a larger lower end and a smaller upper end, the smaller upper end is connected to the push wing, and the push wing extends from the small upper end of the central rod towards the larger lower end so that said push wing will be flexibly attached onto said central rod and is flushed with outer side of the larger end of the central rod when said hook unit is driven into a receptacle.