The "U" BRACE EVACUTAION is a must have for your preschool or daycare! More rugged than traditional individual easy-roll 4" lockable ball-bearing fire casters. Braces attach to underside of crib and legs for additional support. Set of two red,  U-shaped braces. Fits crib models: WB4500, WB4600, WB4503, WB4504, WB4603. 23 1/2" wide x 18" high x 1" deep