Aluminum plank stair treads can be furnished as fabricated from full and partial plank sections with end plates and nosings or as individual extrusions with welded end plates, referred to as Type "F" treads. Type "F" treads are produced from a high-strength aluminum alloy, and meet requirements as specified by BuShips Hull Type plan BU-No. 1604-860041. Type "F" treads are 1-3/4" deep and are available in widths of 4", 6" or 9". The top surface can be supplied unpunched, or with a rectangular punched upset pattern. Type "F" treads are generally used for shipboard application, however, they can also provide safe, serviceable steps for ladder in sewage disposal, chemical and power plants, and refineries.