This 260mm long Picatinny / weaver rail has a flat base bottom. Great length for those project jobs on rifles or shotguns for scopes, laser, flash light, bipod etc. Its made of black alloy so you can custom cut and drill holes to suit your specific requirement and even cut into several rails. Dimentions: 260mm long x 21mm wide, 9.6mm high. I have 222 Loctite listed and its recommended to use on the screws.