602205 Disclosed is a drive assembly for a drug delivery device. A drive assembly for a drug delivery device comprises a guide nut (4) a locking means (9) a body a piston rod a cartridge holder (2) a fastener (14) and a screw thread (8). The guide nut (4), which is a toothed wheel with interspaces, is rotatable around an axis of assembly and engages with the locking means (9). The locking means (9) is a mounted pawl or cantilever to inhibit rotation of the guide nut (4). The guide nut (4) and locking means (9) are arranged in the body. The locking means (9) is fastened to the body. The cartridge holder (2) is removable from the body. The fastener (14) is part of or fastened to the cartridge holder (2). The fastener (14) moves the locking means (9) radially with respect to the axis engaging the locking means (9) with the guide nut (4) when the cartridge holder (2) is attached to the body. The locking means (9) is held in a position so that the locking means (9) is engaged with the guide nut (4) for drug delivery. The screw thread (8) is couples the guide nut (4) and piston rod and enables a helical movement comprising a rotation and a simultaneous shift along the axis. The fastener (14) is a protruding part of the cartridge holder (2) and slides over the locking means (9) to engage the locking means (9) with the guide nut (4) by rotation of the cartridge holder (2).
