The Included U Bolts fit around a 2 inch wide by 3 inch tall cross member. The U Bolts measure 1/2" in diameter, 3" wide, by 3 5/16" long. This Vertical style bunk bracket is the industry standard 8" height, and is designed to mount your Boat Trailer Bunk Boards Vertically. The Brackets and U Bolts are made of a Heavy Duty Galvanized Metal to help Protect against corrosion and Rust. This Kit is ideal for Salt or Fresh Water Boat Trailers. This Kit includes everything needed to complete your bunk board project! Out of the box you'll get the Galvanized Brackets, Mounting U Bolts and Hardware to attach it to your Trailer, as well as a 3/8 inch x 3 inch long Bolt to secure your Bunk Boards. When looking for the best, get something Sturdy Built. Ideal for saltwater or freshwater use, this galvanized kit contains everything you need to mount your bunk boards (not included). These bunk brackets mount with the flat surface facing your boat trailers cross braces. The galvanized u bolts wrap around the brace, and the washers and nut secure the bracket in place. The slotted holes in the bunk support allow for height adjustment. These brackets mount your bunk boards vertically. Includes: Vertical slotted bunk brackets, zinc plated bunk bracket bolts, galvanized mounting U-bolts for the brackets and galvanized U Bolt hardware.