Abstract: In a syringe, in which a needle assembly is engaged by a plunger and withdrawn into a syringe barrel for safe disposal, the plunger slides in a resilient insert secured at the proximal end of the barrel. The insert engages an annular ridge near the distal end of the plunger when the plunger, with the needle assembly attached to it, is fully withdrawn, thereby securely locking the plunger to the barrel, and reliably preventing distal movement of the plunger after the needle assembly is withdrawn into the interior of the barrel. The part of the plunger that protrudes proximally from the barrel may then be snapped off.

Abstract: A syringe, in which a needle assembly is engaged by a plunger and withdrawn into a syringe barrel for safe disposal, incorporates three principal features. A locking tab, hinged to a finger flange, cooperates with a notch in the plunger to prevent inadvertent connection of the plunger to the needle assembly. The needle base has a barbed projection which pierces a hollow stopper on the plunger and is firmly engaged by resilient fingers located inside the stopper. The plunger slides in a resilient insert secured at the proximal end of the barrel. The insert engages an annular ridge near the distal end of the plunger when the plunger, with the needle assembly attached to it, is fully withdrawn, thereby securely locking the plunger to the barrel, and reliably preventing distal movement of the plunger after the needle assembly is withdrawn into the interior of the barrel. The part of the plunger that protrudes proximally from the barrel may then be snapped off.