American Defense Mounts will fit both Picatinny and Weaver rails. Our standard cross bolt width is .203″, made for milspec picatinny rails. We do offer a smaller bolt that is .187″ wide. Our mounts will fit some, but not all weaver rails. If the recoil lug width on the weaver rail is greater than .187″ our smaller .187″ bolt will work. If the width is smaller, the .187 bolt will not fit the weaver rail. We do have the ability to modify our bolt to fit your weaver rail, we just need to know the width it needs to be. If you would like to order your mount with the .187″ bolt, please contact Sales@americandefensemfg.com