The Backrack Toolbox Hardware Kit is designed to accommodate a standard 21" cross bed Toolbox. The Toolbox sits on top of the Toolbox Brackets allowing you to slide the Toolbox forward so that bed space is not wasted. The Toolbox is secured to the Toolbox Bracket by drilling sheet metal screws through the Toolbox and into the top of the Toolbox Bracket. Drill and bolt is also acceptable. Clamp hooks that come with the Toolbox are not required. Toolbox Brackets are also available in 31" length as an accessory. Not compatible with Tonneau Cover Adapter Brackets.