Sold individually, not in pairs. Rails designed by Welcome and Professor Paul Schmitt of PS Stix. Only 4 holes as opposed to 5, with high-bite screws that make for very easy installation without a drill. Custom asymmetrical shape and size, which fits modern concaves better than competition. Shape creates better grip for grabs, and height of rail allows for them to be placed further out towards the rail, instead of towards the middle of the board. Vertical groove reduces weight without compromising strength. Super high-molecular-density extruded plastic, comparable to cutting board plastic. Much more durable than injection-molded plastic, which is the current standard. Each rail comes pre-taped with a double-sided foam tape, which creates a better adhesion to the board and also absorbs any rattle sound which might otherwise occur. Made by hand in the U.S. Welcome actually cuts, drills, tapes, and packages the rails in their warehouse in CA.