A sub-assembly of a drug delivery device comprises a propellant comprising a reservoir housing defining a reservoir, a through hole, at least one inlet in fluid communication with the hole, and a stem having an outlet open end in fluid communication with the hole. A source, the stem, relative to the reservoir housing between a first position where at least one inlet is not in fluid communication with the reservoir and a second position where at least one inlet is in fluid communication with the reservoir. The propellant source includes a propellant source that further includes a biasing member for biasing the stem toward the first position. Further, the subassembly is a collet member having a plurality of first radial flexible fingers and a plurality of second radial flexible fingers, each attached to each of the plurality of first and second radial flexible fingers. When not biased, the plurality of first radially flexible fingers includes a collet member that extends radially inward of the plurality of second radial flexible fingers. The plurality of first radially flexible fingers prevents axial movement of the stem relative to the collet member when the stem is axially biased with a force less than the force threshold, but is the stem greater than the force threshold? Or it is configured to engage the stem so as to allow axial movement of the stem relative to the collet member when biased axially with equal force. The plurality of second radially flexible fingers do not prevent axial movement of the stem relative to the collet member when in the radially outward position but engage the stem when in the biased radially inward position Thus, for example, axially by a force that is substantially equal to or greater than the force required to compress the biasing member with the stem being substantially equal to or greater than the force threshold. When energized, it prevents axial movement of the stem relative to the collet member and moves the stem to a second pos
