DRIVE MECHANISM FOR A DRUG DELIVERY DEVICE THE PRESENT INVENTION RELATES TO A DRIVE MECHANISM FOR A DRUG DELIVERY DEVICE AS WELL AS TO A DRUG DELIVERY DEVICE FOR DISPENSING OF A DOSE OF A MEDICINAL PRODUCT, WHEREIN THE DRIVE MECHANISM COMPRISES: A HOLDER (14) FOR A PRODUCT-CONTAINING CARTRIDGE (16), THE CARTRIDGE (16) HAVING A PISTON (18) SLIDABLY ARRANGED THEREIN IN AN AXIAL DIRECTION, A PISTON ROD (26; 48; 52; 62; 76; 92; 116) TO BE OPERABLY ENGAGED WITH THE CARTRIDGE’S PISTON (18) FOR DISPENSING OF A DOSE OF THE MEDICINAL PRODUCT, - AT LEAST ONE ADJUSTING MEMBER (20; 46; 54; 64; 78; 90; 112) SLIDABLY ARRANGED IN AXIAL DIRECTION RELATIVE TO THE PISTON (18) AND/OR RELATIVE TO THE PISTON ROD (26; 48; 52; 62; 76; 92; 116) FOR ELIMINATING AXIAL CLEARANCE (34) BETWEEN THE PISTON (18) AND THE PISTON ROD (26; 48; 52; 62; 76; 92; 116), - AN INTERLOCK MEANS (24; 58; 66; 80; 100) ADAPTED TO INTERACT WITH THE ADJUSTING MEMBER (20; 46; 54; 64; 78; 90; 112) FOR MUTUALLY LOCKING IN POSITION THE PISTON (18) AND THE PISTON ROD (26; 48; 52; 62; 76; 92; 116) IRRESPECTIVE OF THE RELATIVE DISTANCE BETWEEN PISTON (18) AND PISTON ROD (26; 48; 52; 62; 76; 92; 116). THE MOST ILLUSTRATIVE DRAWING IS FIGURE 1.