Atlas Bipods 3.35in Flush Cup 1913 Rail Radius Back hole patterns Black 1.76-2.78in. 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 17) to attach this rail to the forearm of standard rifle stocks. Specifications for Atlas Bipods 3.35in Flush Cup 1913 Rail Radius Back hole patterns: Manufacturer: Atlas Bipods Color: Black Country of Origin: USA Package Contents: Atlas Bipods 3.35in Flush Cup 1913 Rail Radius Back hole patterns Atlas Bipods BT15 3.35in Flush Cup 1913 Rail Radius Back hole patterns Black 1.76-2.78in