B&T Industries 3.35" Flush Cup 1913 Rail: radius back, center-to-center hole spacing of 1.76 - 2.78" approx. BT15
B&T Industries 3.35" Flush Cup 1913 Rail: radius back, center-to-center hole spacing of 1.76 - 2.78" approx. BT15, The Atlas BT15 3.35" M1913 rail will work with hole spacing of 1.76 - 2.78" with a relieved base to accommodate curved surfaces.