A controllable coupling assembly (10, 300, 400) having forward and reverse backlash, the assembly (10, 200, 400) comprising: a plurality of forward locking elements, each of the forward locking elements having a load-bearing surface; at least one reverse locking element; and first and second coupling members (34, 58, 302, 402) supported for relative rotation about a common rotational axis, the coupling members (34, 58, 302, 402) including: a first coupling face having a set of forward pockets (52, 410) angularly spaced about the axis, each of the forward pockets (52, 410) receiving one of the forward locking elements and defining a forward load-bearing surface adapted for abutting engagement with the load-bearing surface of its respective forward locking elements; a second coupling face having a set of reverse locking formations adapted for abutting engagement with the at least one reverse locking element to prevent the relative rotation in a reverse direction about the axis; and a third coupling face that opposes the first coupling face, the third coupling face having a set of forward locking formations (60, 310), each of the set of forward locking formations (60, 310) being adapted for abutting engagement with one of the forward locking elements to prevent the relative rotation in a forward direction about the axis, wherein the number of forward locking elements is different than the number of reverse locking elements; characterised in that the number of forward locking formations (60, 310) is different than the number of reverse locking formations and in that either the forward backlash is a non-zero integer multiple of the reverse backlash or the reverse backlash is a non-zero integer multiple of the forward backlash to prevent the coupling assembly (10, 300, 400) from inadvertently binding in both directions about the axis. a plurality of forward locking elements, each of the forward locking elements having a load-bearing surface; at least one reverse locking element; and first and second coupling members (34, 58, 302, 402) supported for relative rotation about a common rotational axis, the coupling members (34, 58, 302, 402) including: a first coupling face having a set of forward pockets (52, 410) angularly spaced about the axis, each of the forward pockets (52, 410) receiving one of the forward locking elements and defining a forward load-bearing surface adapted for abutting engagement with the load-bearing surface of its respective forward locking elements; a second coupling face having a set of reverse locking formations adapted for abutting engagement with the at least one reverse locking element to prevent the relative rotation in a reverse direction about the axis; and a third coupling face that opposes the first coupling face, the third coupling face having a set of forward locking formations (60, 310), each of the set of forward locking formations (60, 310) being adapted for abutting engagement with one of the forward locking elements to prevent the relative rotation in a forward direction about the axis, wherein the number of forward locking elements is different than the number of reverse locking elements; characterised in that the number of forward locking formations (60, 310) is different than the number of reverse locking formations and in that either the forward backlash is a non-zero integer multiple of the reverse backlash or the reverse backlash is a non-zero integer multiple of the forward backlash to prevent the coupling assembly (10, 300, 400) from inadvertently binding in both directions about the axis. a first coupling face having a set of forward pockets (52, 410) angularly spaced about the axis, each of the forward pockets (52, 410) receiving one of the forward locking elements and defining a forward load-bearing surface adapted for abutting engagement with the load-bearing surface of its respective forward locking elements; a second coupling face having a set of reverse locking formations adapted for abutting engagement with the at least one reverse locking element to prevent the relative rotation in a reverse direction about the axis; and a third coupling face that opposes the first coupling face, the third coupling face having a set of forward locking formations (60, 310), each of the set of forward locking formations (60, 310) being adapted for abutting engagement with one of the forward locking elements to prevent the relative rotation in a forward direction about the axis, wherein the number of forward locking elements is different than the number of reverse locking elements; characterised in that the number of forward locking formations (60, 310) is different than the number of reverse locking formations and in that either the forward backlash is a non-zero integer multiple of the reverse backlash or the reverse backlash is a non-zero integer multiple of the forward backlash to prevent the coupling assembly (10, 300, 400) from inadvertently binding in both directions about the axis.