This heavy duty Aluminum hat bracket is a perfect replacement for aluminum boat trailers. It is made out of aluminum that is 3/8 inch thick at the mounting surface and a 1/4 inch thick on the bottom plate. It can be used in conjunction with a V-guide set up or bunk board supports. Typically this item will fit on a trailers cross member that is 3 inch x 3 inch square tube. The hole spacing center hole to center hole measures 3 5/8 inch. You will need to use a u-bolt that is 1/2 inch diameter and 3 inch wide on the inside. This hat bracket is used to clamp front v-guides or bunk boards that use 2 inch x 2 inch square tubing for their support. The correct sized U-Bolt for mounting this support to your trailer would be the Stainless Steel U-Bolt 1/2 inch x 3 inch x 4 5/16 inch Trailer U-Bolt. This will allow you to snugly mount whichever apparatus you in tend to and have a permanent replacement that will not rust.