3 Space 1/8" aluminum rack panel with a steel back box, 5" deep. Rack panel is 19" wide x 5-1/4" tall, 18 ga. steel back box is 17-3/16" wide x 5" tall and 5" deep. Inside dimensions are 17-5/64" wide x 4-29/32" tall x 4-15/16" deep. Powder coated black.