Lancer 4 Inch Accessory Rail with Backing Hardware are precision machined aluminum Picatinny design. The 4 inch accessory rails are different from the slight rail. They are a little thicker and are designed to be used with the provided backer plates and fasteners. The backer plates are designed to lock into the cooling slots, providing positive retention during rough handling. The Lancer Accessory Rail with backing hardware weight 1.4 ounces.