Fitment - RV bumper mount holder compatible with Rhino Tote Tank sizes (15, 21, 28, and 36 gallons), and most other portable waste holding tanks on the market. Standard Square Rv Bumpers - Bumper Mount Tote Tank Holder fits 4-inch and 4-1/2-inch bumpersIdeal for RVs without ladders. High Quality - Portable rv waste tank rack is constructed of sturdy, durable steel with a black powder-coated finish that resists rain, mud, dirt and other external elements. More External Storage - RV Portable Tank Holder securely attaches your portable tank to a standard RV bumper, also includes straps to hold portable tanks in place. Package Includes - two L brackets, two mounting plates, two straps, four u-bolts, eight locknuts, eight spacers (Note: locknuts need to be tightened with a wrench, tightening can effectively prevent falling off)