This base is designed to hold multiple targets with an AR500 BAR that replaces the 2×4’s, or you can use 2×4’s to mount or you can also use paper targets with the 1×2 cut out slot. Very durable and sturdy. Breaks down to fit in a back back for easy transport. Also no hardware needed!! All parts interact constructing this amazing base with multiple functions. 2×4 sizes do vary, if the 2×4 is a tight fit shaving off the end will work. Making the 2×4 slot too loose will cause lean/pitch issues.