The connection joint attaching the needle assembly to the hypodermic syringe includes a female conical opening in the reduced boss of the barrel and a male conical extension of the hub which corresponds in dimensions such that when the conical extension is inserted into the conical opening, the proximal end of the extension will be substantially flush with the inner end wall of the barrel. At the same time, a substantially leakproof seal between such conical surfaces is provided whereby there will be no residual volume of liquid beyond the measured amount in the barrel when a piston is extended fully into the barrel against the end wall and there will be no leakage of the liquid between the juncture of such conical surfaces. A tubular collar is provided with an inwardly extending radial ring or bead which firmly and frictionally engages with the outer surfaces of the reduced boss on the syringe barrel to provide a mechanical lock of the needle assembly. In time, the radial bead forms a corresponding depression or detent in the outer surface of the reduced boss thereby preventing the needle assembly from disassociating with the syringe barrel either during removal of the needle sheath or during the liquid injection process.