RV 4" Square Bumper-Mounted Cargo Box Support Arms (TM) Fits 4" x 4" Square Bumper | Make your own RV bumper-mounted cargo carrier with these tray arms. Each pair of steel cargo carrier support arms weighs 10 pounds and carries 200 pounds Use multiple sets of these steel cargo carrier support arms to carry more weight Cargo carrier support arms clamp tight to 4 inch square RV bumper, eliminating shake, rattle, and roll found in hitch-mounted cargo carriers We sandblast, primer, and powder coat all of our steel products to ensure a long-lasting finish