Sub-assembly for a medicament delivery device, medicament delivery device, and method for operating a medicament delivery device

A sub-assembly for a medicament delivery device, extending along a longitudinal axis between a proximal end and a distal end, the sub-assembly comprising:

• an enclosure;
• a lock bracket arranged in and rotatable relative to the enclosure;
• a plunger rod configured to act on a stopper of a cartridge of the medicament delivery device containing a medicament;
• and
• a plunger rod spring arranged between the plunger rod and the lock bracket, wherein the plunger rod spring is configured to move the plunger rod from a distal position to a proximal position relative to the enclosure,
• wherein the lock bracket comprises:
• a mechanical interface portion configured to engage with a corresponding mechanical interface portion of the enclosure for effecting a rotation of the lock bracket relative to the enclosure and around the longitudinal axis;
• and
• a flexible arm extending in the direction of the longitudinal axis along a portion of the plunger rod, wherein the flexible arm comprises a distally directed surface, wherein the flexible arm is configured to flex radially inwardly relative to the enclosure from a first position where the distally directed surface of the flexible arm is engaged with a proximally directed surface of the enclosure to a second position where the distally directed surface of the flexible arm is disengaged with the proximally directed surface of the enclosure,
• wherein the plunger rod is radially lined up with the flexible arm when the plunger rod is in the distal position so that the flexible arm is blocked from moving into the second position and spaced apart from the flexible arm when the plunger rod is in the proximal position such that the flexible arm flexes in the second position, such that the plunger rod spring pushing the lock bracket in the distal direction to interact with the mechanical interface portions and effecting the rotation of the lock bracket relative to the enclosure.