A clutch mechanism 5 for use with a carrier of a linear drive device 1, the mechanism 5 comprising: a housing 3; a first gear 6 coupled to the housing 3 and having gear teeth 61 configured to engage athreaded shaft 2 of a linear drive device 1, such that rotation of the shaft 2 causes the housing 3 to move along the shaft 2 in a first mode of operation; and a first clutch arrangement associated w ith the first gear 6 and configured to prevent substantial rotation of the first gear 6 with respect to the housing 3 when a rotational force applied to the first gear 6 is less than a threshold forceand to permit rotation of the first gear 6 with respect to the housing 3 when a rotational force applied to the first gear 6 is greater than the threshold force, such that the housing 3 can be manual ly moved along a length of the shaft 2, in a second mode of operation, by exerting a force on the housing 2 such that the rotational force applied to the first gear 6 through the interaction of the threaded shaft 2 and the gear teeth exceeds the first threshold.