An apparatus (100, 200) for supporting an object, the apparatus comprising: a support surface; a first retainer (110, 210, 310, 410, 710, 910, 1010) and a second retainer (120, 220, 320, 420, 720, 920, 1020), the first retainer being for coupling at least in part by the support surface to the second retainer, or being coupled at least in part by the support surface to the second retainer, wherein at least one of the first and second retainers comprises a stop (112, 122, 212, 222, 312, 322, 412, 422, 712, 722, 912, 922); a fastener, comprising: an outer part including an internal surface that comprises a threaded portion wherein the internal surface of the outer part is an internal surface of a through hole extending through the outer part; and an inner part (150, 350, 450, 550, 650, 750, 850, 950) including an external thread (152, 352, 552, 652, 752, 852, 952) arranged to enable the outer part to threadably rotate around the inner part, and at least one slot (154, 354, 454, 554, 654, 754, 757, 759, 854, 857, 859, 954, 957, 959) having a non-circular cross section in a plane perpendicular to the screw axis of the external thread, the at least one slot being shaped to receive the first and second retainers, such that the first and second retainers are rotatably fixed relative to the at least one slot and the stop prevents the retainers from exiting the at least one slot in a direction co-incident with or parallel to the screw axis. a support surface; a first retainer (110, 210, 310, 410, 710, 910, 1010) and a second retainer (120, 220, 320, 420, 720, 920, 1020), the first retainer being for coupling at least in part by the support surface to the second retainer, or being coupled at least in part by the support surface to the second retainer, wherein at least one of the first and second retainers comprises a stop (112, 122, 212, 222, 312, 322, 412, 422, 712, 722, 912, 922); a fastener, comprising: an outer part including an internal surface that comprises a threaded portion wherein the internal surface of the outer part is an internal surface of a through hole extending through the outer part; and an inner part (150, 350, 450, 550, 650, 750, 850, 950) including an external thread (152, 352, 552, 652, 752, 852, 952) arranged to enable the outer part to threadably rotate around the inner part, and at least one slot (154, 354, 454, 554, 654, 754, 757, 759, 854, 857, 859, 954, 957, 959) having a non-circular cross section in a plane perpendicular to the screw axis of the external thread, the at least one slot being shaped to receive the first and second retainers, such that the first and second retainers are rotatably fixed relative to the at least one slot and the stop prevents the retainers from exiting the at least one slot in a direction co-incident with or parallel to the screw axis. an outer part including an internal surface that comprises a threaded portion wherein the internal surface of the outer part is an internal surface of a through hole extending through the outer part; and an inner part (150, 350, 450, 550, 650, 750, 850, 950) including an external thread (152, 352, 552, 652, 752, 852, 952) arranged to enable the outer part to threadably rotate around the inner part, and at least one slot (154, 354, 454, 554, 654, 754, 757, 759, 854, 857, 859, 954, 957, 959) having a non-circular cross section in a plane perpendicular to the screw axis of the external thread, the at least one slot being shaped to receive the first and second retainers, such that the first and second retainers are rotatably fixed relative to the at least one slot and the stop prevents the retainers from exiting the at least one slot in a direction co-incident with or parallel to the screw axis.