The Atlas Flush Cup 3.35" 1913 Rail will accommodate hole patterns with a center to center spacing of 1.76 – 2.78" with a relieved base to accommodate curved surfaces. A standard sling stud and sling stud spacer can be used as one fastener or two button head machine screws can be used. NO HARDWARE IS INCLUDED (see P/N 640382) to attach this rail to the forearm of standard rifle stocks. The Atlas Flush Cup 1913 Rail can also be attached to a horizontal surface on the butt section to attach their BT12 or BT13 Precision Rail Monopods. This rail also has a flush cup for that style of sling swivels.