The arms are height adjustable Steel with 4 pair 18" arms + 4 pair 24" arms + 4 castors(Two Swivel With Brake). Body Moldings & Trims. 1 X Bumper Storage Rack. Fairings & Body Work. High-strength steel structure: Made of high-quality steel to ensure the sturdiness and durability of the rack, able to withstand the weight of heavy-duty bumpers.