The new BT17 – 4″ 1913 Rail will accommodate hole patterns with a center to center spacing of 2.2 – 3.5″ with a FLAT base to accommodate flat surfaces. A standard sling stud can be used as one fastener or two Button head machine screws can be used (not included) to attach this rail to the forearm of standard rifle stocks. The BT17 can also be attached to a horizontal surface on the Butt section to attach our BR12 or BT13 Precision Rail Monopods. The BT17 also has a flush cup for that style of sling swivels.