Sub-assembly of a medicament delivery device and a medicament delivery device

A sub-assembly of a medicament delivery device, the sub-assembly comprising:

• a plunger rod comprising an outer surface, where the plunger rod is biased;
• a main body extending longitudinally to partially surround the outer surface of the plunger rod, where the main body comprises a flexible arm that is directly and releasably connected to the outer surface of the biased plunger rod;
• and
• a coupling member axially fixed, partially surrounding, and rotatable relative to an outside surface of the main body such that the outside surface of the main body is between the outer surface of the plunger rod and an inner surface of the coupling member when the coupling member rotates from a first position to a second position, where the inner surface of the coupling member confines the flexible arm in a locking engagement with the outer surface of the plunger rod to prevent axial movement of the plunger rod when the coupling member is in the first position,
• wherein the main body comprises a first locking element and the coupling member comprises a second locking element having a protrusion extending radially inward from an inner surface of the coupling member,
• wherein rotation of the coupling member from the first position causes the first locking element and the second locking element to be releasably engaged with each other such that the coupling member is prevented from rotating to an axial release position relative to the main body, and
• wherein movement of the coupling member to the second position allows the flexible arm to disengage from and unlock the plunger rod,
• wherein the first locking element extends in an axial direction from the main body, then extends radially outwards in an arch, and then extends radially inwards so that a free end of the first locking element is engaged with the second locking element to prevent the coupling member from rotating relative to the main body.