ATLAS BIPOD 1913 PICATINNY RAIL Atlas 1913 Rails serve as attachment points for Atlas Bipods that fit Picatinny rails. 3.35" rail accommodates hole patterns with 1.76" to 2.78" center-to-center spacing and fits onto curved surfaces. 4" rail accommodates hole patterns with 2.2" to 3.5" center-to-center spacing and fits onto flat surfaces. Rails attach to the stock with either a sling stud and spacer or machine screws, (not included). Mfg: Accu-Shot