A single-use syringe of the self-destructible or passiveself-lockable type, namely in which self-locking thereofoccurs after the syringe has been used a first time,independently of the user's will, is characterised in thatit comprises at least two rings on the inner side of thebarrel which have the general shape of a circular rim witha variable inner radius and in that each one of thelongitudinal ribs of the plunger has a height which isdifferent from that of at least one of the other ribs sothat the plunger can be inserted in a close-fitting mannerthrough the space defined by the variable inner radius ofthe barrel rings. In this way the resistance to passageof the plunger is miminised, reducing the risk offormation of haematomas, and with a manufacturing costsubstantially similar to that of conventional syringes.
