A sub-assembly (12, Fig 1) of a medicament delivery device (10, Fig 1), wherein the sub-assembly comprises a propellant source 26 which includes a reservoir housing 44 to define a reservoir 46 and a stem 48 with a bore 50 therethrough. The stem has least one inlet 52 in fluid communication with the bore, and an open outlet end 54 in fluid communication with the bore. The stem is moveable relative to the reservoir housing between a first position (Fig 4) in which the at least one inlet is not in fluid communication with the reservoir and a second position (Fig 5) in which the at least one inlet is in fluid communication with the bore. The propellant source further comprises a biasing member 56 for biasing the stem towards the first position. The sub-assembly also includes a collet member 20 with two sets of radially flexible fingers 62, 64. The fingers 62, 63 are arranged to inhibit the stem in different positions.
