Prebend spreaders raked aft. These arms are simply pinned to the mast flange and to a small plate of aluminum at the tips (under the black tape). There is a slot in the very end of the plate to accept the diamond cable. A plastic roller is also positioned above the arm to help prevent the jib from abraiding/snagging during tacks. The forward arm is threaded where it attaches to the mast flange so that its length is adjustable. This sets the amount of arm sweep in the system. A flat batten placed across the tips is measured to the mast track edge to set the arm rake. Typically 1-2.5 inch ranges are used, depending on crew weight, weather/sea conditions, sail cut etc. More rake induces more mast bend in the long axis of the mast...thus flattening the sail more. A flatter sail is more efficient, but less powerful.