The invention relates to a detent mechanism (18) for controlling translation between two components (2, 7) in a longitudinal direction (P, D), the detent mechanism (18) comprising at least one clip (7.12, 2.6) on one of the components (2, 7) arranged to be in a ramped engagement with a recess in the other one of the components (7, 2) in an initial state in such a manner that translation between the components (2, 7) is constrained and that application of a translative force between the components (2, 7) in one longitudinal direction (P, D) with the clip (7.12, 2.6) engaged with the recess deflects the clip (7.12, 2.6) out of the recess when a predetermined value of the translative force, at least depending on the resilience of the clip (7.12, 2.6), is overcome so as to allow translation between the components (2, 7).
