Clamps directly to the underside of a steel I-beam on your studio ceiling. Adjusts to fit beams measuring 2 1/2" to 8" (6 to 20cm) wide and from 1/8" to 1/2" (3 to 12mm) thick. When the clamp is installed, the rails will run at a 90° angle to the supporting I-beam. If the rails are intended to run parallel to the supporting I-beam, a Back-to-Back Rail Clamp is required for each girder clamp. One clamp is needed for every 3' (91cm) of rail to be mounted to the ceiling.