1. A piston for a cartridge (24) for the delivery of drugs device comprising:- At least one annular sealing surface (35) in contact with the radially inner side wall (24) of the cartridge (33),- A distal surface (42) to limit the volume of the cartridge (33), receiving the medicament- The surface (40) adapted to receive the plunger applies an axial force (10, 32) a drug delivery device for the displacement of the piston in a proximal direction relative to the side wall (24) receiving the axial force,- While receiving thrust surface (40) comprises a plurality of centering elements (34) projecting from the receiving axial surface force (40) towards the plunger (10, 32), and wherein the centering elements (34) have an outer shape and geometry, which coincide with the corresponding receptacle (38) of the plunger (10, 32), and wherein the centering elements (34) having an arcuate shape in a plane parallel to the receiving axial surface force (40), positioned and aligned circumferentially imaginary annular or circular structure characterized in that at least one centering element has golovkoobraznuyu form.2. A piston according to claim 1, wherein the centering elements (34) and / or circular structure consistent circular shape receptacle (38) of the plunger (32).3. Piston according to claim 1, wherein the at least one centering element (34) is formed integrally with the housing (36) of the piston.4. A piston according to claim 1, wherein the at least one centering element (34) tapers in the direction of the plunger (10, 32).5. A piston according to claim 1, wherein the at least one centering element (34) comprises a bevelled transverse surface (46) disposed at an angle of from 20 ° to 80 ° relative to the plane of the receiving surface of the axial force (40).6. A piston according to claim 1, wherein the at least one centering element (34) has a triangular or convex shape in a plane perpendicular to the receiving surface of the axial force (40).7. Piston according to any
