521 Series is a sectional aluminum door appropriate for environments where maximum light infiltration and/or visual access is required. Designed to fit openings up to 26'2" (7976 mm) wide and 20'1" (6121mm) high, the 521 Series features a wide, 2-3/4" (70mm) center stile, 3-3/4" (95mm) or 4-1/2" (114mm) bottom rail, based on door size.