Flat Lateral Hip/Thigh Supports mounted from the seat provides lateral control of the pelvis as well as queing for midline positioning of the pelvis, and in the case of a longer pad, will also offer lateral control of the femors to prevent abducting. When ordering this accessory, you must choose a mounting hardware option. If this positioning pad is to be mounted by Biodynamics on a Bio-ST seat or back, black aluminum tracks will be provided to allow for maximum adjustability. If this positioning pad is to be mounted by Biodynamics on a Bio-ST-HD seat or back, a rounded groove in the interface plate will be installed to provide maximum adjustability