These tie-downs are for securing all of types of light or heavy loads and/or equipment. When installed, the surface is flush with the bed of your truck or trailer. Each tie-down D-ring includes a large backer plate that helps to solidify and protect the bed material, while adding strength and rigidity. Included in this set: 6 - Heavy-Duty (6,000 pound rating) recessed pan D-rings 6 - Over-sized backer plates (6 1/2" x 6 1/2") 24 - 3/8" x 2 1/2" Grade 5, zinc-plated, carriage bolts 24 - 3/8" zinc-plated flat washers 24 - 3/8" Grade 8, zinc-plated, nylon lock nuts Detailed DIY installation guide Weather Resistant Zinc Plating: This set of D-Rings and all of the included hardware are zinc-plated for corrosion resistance and excellent protection from the elements. Heavy-Duty Construction for the Toughest Hauling Jobs: This set is simple enough to handle small tie-down jobs and tough enough to handle larger loads. Each D-Ring has a load rating of 6,000 pounds. Our large (6 1/2" x 6 1/2") heavy-duty backer plate adds additional protection and rigidity, preventing tear-through of your bed material. High-quality mounting hardware is made from tough Grade 5 and Grade 8 steel. Nylon-insert lock nuts assures your mounting will stay tight even with road vibrations. The 2 1/2" carriage bolts can accommodate truck and trailer beds up to 1 5/8" thick. Includes DIY Easy-To-Follow Installation Guide We've included an installation guide that helps to walk you through the installation process, including recommended hole sizes, tool sizes and layout guidelines. For easiest installation, we recommend having the following tools: Electric Drill 1/2" drill bit (15/32" could work, but requires more precision) 3 1/2" whole saw (3 1/4" could work, but requires some extra routing/chiseling) 9/16" wrench (a deep socket or ratchet wrench makes things go easier/quicker)