These 55 Series aluminum seats that replace Kirkey 41 Series seats are constructed from .100" thick 5052 aluminum. Extra strength and safety is a result of an offset aluminum extrusion around the perimeter of the seat. Manufactured with double shoulder belt openings and sub belt openings with molded rubber inserts that will accommodate all belt systems. The 18-1/2" and 20" sizes feature longer bottom, sub belt and lap belt openings moved forward, side bolsters and rear belt openings raised to accommodate larger drivers. Covers and seat mounts sold separately.