A drive member and a rotation member are rotatable with respect to a housing. The drive member comprises drive fingers, which are resilient or resiliently mounted. A slider is disposed at the drive member and is axially movable between a first position, in which the slider keeps the drive fingers constrained, and a second position, in which the drive fingers are released. A unidirectional rotational clutch engages the drive member with the rotation member. The clutch is formed by the drive fingers when the slider is in the first position. The drive member and the rotation member are disengaged when the slider is in the second position. The slider is in the first position when a unit is attached to the housing, and in the second position when the unit is removed.