US Patent 7192418 Disposable syringe

A disposable syringe has a needle seat with an upper segment adapted to be fitted with a needle cannula, and a lower segment retained in a passage of a barrel. A plunger has a stem portion movable in the passage, a deformable surrounding engaging portion in sealing contact with the passage so as to be moved by the stem portion to a position of use, and a surrounding abutting head which is moved towards and which is held by a grip segment in the needle seat when the surrounding engaging portion is depressed by an edge portion of the needle seat by virtue of a continuing depression force of the plunger, thereby permitting the needle seat to be brought into the passage for disposal.