A sub-assembly of a medicament delivery device, the sub-assembly comprising including a propellant source having a reservoir housing defining a reservoir and a stem having a bore therethrough, at least one inlet in fluid communication with the bore, and an open outlet end in fluid communication with the bore, the stein being moveable relative to the reservoir housing between a first position in which the at least one inlet is not in fluid communication with the reservoir and a second position in which the at least one inlet is in fluid communication with the reservoir, the propellant source further including a biasing member for biasing the stem towards the first position. The sub-assembly further including a collet member having a first plurality of radially flexible fingers and a second plurality of radially flexible fingers.