Various embodiments of piston rod assemblies, drug delivery devices making use of such piston rod assemblies, and methods for assembling such piston rod assemblies and drug delivery devices are provided. In one embodiment, a piston rod assembly for a drug delivery device is provided, wherein the piston rod assembly is configured to engage a piston of a medicament cartridge. The piston rod assembly comprises (i) a piston rod, (ii) at least one adjusting member displaceably engaged with a distal end section of the piston rod, wherein the at least one adjusting member is displaceable along a long axis of the piston rod, and (iii) at least one interlock member configured to mutually lock the at least one adjusting member and the piston rod in an arbitrary relative axial position.