Models : - 531818C : cushion with cover 18" x 18" - 11.1655 : cushion without cover 16" x 16" - 5300C : cushion with cover 16" x 16" - 11.1656 : cushion without cover 18" x 16" - 5301C : cushion with cover 18" x 16" - 11.1699 : cushion without cover 18" x 18"