The RES (Rail Expansion System) is a slotted rail that works with any Pace Edwards Rack, Thule or Yakima rack. This handy feature allows kayaks, bicycles, cargo baskets and more to be carried without compromising use of the cover and bed. The intermittent locking functionality is a handy feature that will automatically engage every 12 inches. Easily carry taller items without leaving the rest of the bed exposed. Extruded aluminum panels with a heavy-duty, black powder coat finish gives the UltraGroove Metal tonneau cover a clean yet rugged metal finish. Pace Edwards utilizes a pull strap to make it easy to open and close the tonneau cover from the tailgate. No need to walk around the truck bed. The Continuous Tension Spring creates a smooth pull on the cover to retract it into the canister. The rails work like gutters to channel water away from the bed via the drain tubes. Two sets of drain tubes are included for the front and rear of the bed. Some vehicles may require drilling for the drain tubes. There is a rear seal that rests on top of the tailgate, and extended rail caps create a seal for the rear corners of the bed. Pace Edwards uses turn-knob clamps, for most vehicles, that remove the need for a wrench. These clamps can be tightened down by hand for a simple, efficient rail installation. No drilling required on most vehicles.