A threaded coupling comprising: a first coupling member, comprising a cylindrical portion which is internally threaded around an axis of rotational symmetry of the cylindrical portion and comprises an open end that defines an opening with an annular rim, the annular rim comprising at least one projection (18, 710) that projects in a generally axial direction parallel to the axis of rotational symmetry of the cylindrical portion; a second coupling member comprising an externally threaded portion and at least one key cavity (14., 506); and a locking assembly comprising: a locking member (500, 700, 800) comprising a pin portion (9, 502, 702, 802) fixed to a flexible cable portion (8, 704, 804); and a lock nut; wherein the externally threaded portion is arranged to be received through the opening to be threadedly engaged with the internally threaded cylindrical portion, to couple the first coupling member to the second coupling member; and wherein, when the first coupling member is coupled to the second coupling member: the pin portion (9, 502, 702, 802) is arranged to be seated in the at least one key cavity (14, 506, 706) and be confined by an inner surface of the annular rim so as to restrict radial movement of the pin portion (9, 502, 702, 802); the lock nut is arranged to be threaded onto the second coupling member and positioned so as to restrict axial movement of the pin portion (9, 502, 702, 802); and characterised in that, when the first coupling member is coupled to the second coupling member, the flexible cable portion (8, 704, 804) is arranged to extend from the pin portion (9, 502, 702, 802) in a generally radial direction adjacent to a surface of the at least one projection (18, 710) of the annular rim so as to restrict circumferential movement of the flexible cable portion (8, 704, 804). a first coupling member, comprising a cylindrical portion which is internally threaded around an axis of rotational symmetry of the cylindrical portion and comprises an open end that defines an opening with an annular rim, the annular rim comprising at least one projection (18, 710) that projects in a generally axial direction parallel to the axis of rotational symmetry of the cylindrical portion; a second coupling member comprising an externally threaded portion and at least one key cavity (14., 506); and a locking assembly comprising: a locking member (500, 700, 800) comprising a pin portion (9, 502, 702, 802) fixed to a flexible cable portion (8, 704, 804); and a lock nut; a locking member (500, 700, 800) comprising a pin portion (9, 502, 702, 802) fixed to a flexible cable portion (8, 704, 804); and a lock nut; wherein the externally threaded portion is arranged to be received through the opening to be threadedly engaged with the internally threaded cylindrical portion, to couple the first coupling member to the second coupling member; and wherein, when the first coupling member is coupled to the second coupling member: the pin portion (9, 502, 702, 802) is arranged to be seated in the at least one key cavity (14, 506, 706) and be confined by an inner surface of the annular rim so as to restrict radial movement of the pin portion (9, 502, 702, 802); the lock nut is arranged to be threaded onto the second coupling member and positioned so as to restrict axial movement of the pin portion (9, 502, 702, 802); and characterised in that, when the first coupling member is coupled to the second coupling member, the flexible cable portion (8, 704, 804) is arranged to extend from the pin portion (9, 502, 702, 802) in a generally radial direction adjacent to a surface of the at least one projection (18, 710) of the annular rim so as to restrict circumferential movement of the flexible cable portion (8, 704, 804). the pin portion (9, 502, 702, 802) is arranged to be seated in the at least one key cavity (14, 506, 706) and be confined by an inner surface of the annular rim so as to restrict radial movement of the pin portion (9, 502, 702, 802); the lock nut is arranged to be threaded onto the second coupling member and positioned so as to restrict axial movement of the pin portion (9, 502, 702, 802); and characterised in that, when the first coupling member is coupled to the second coupling member, the flexible cable portion (8, 704, 804) is arranged to extend from the pin portion (9, 502, 702, 802) in a generally radial direction adjacent to a surface of the at least one projection (18, 710) of the annular rim so as to restrict circumferential movement of the flexible cable portion (8, 704, 804).