Slotted rails are mounted to the tops of the sides, ends and tailgate of a pickup truck box. Each rail has an outwardly extending flange resting on the top of the truck box. The rails are fastened to the box by screws extending through holes in the rails and outwardly into the inside wall of the truck box at the sides and ends. There are longitudinally spaced slots in the rail above the flange. An outwardly opening longitudinally extending groove in the flange receives and secures a reinforced hem of a tonneau cover. One embodiment of the rail has a longitudinally extending downwardly opening groove in the bottom of the rail receiving the upper edge portion of a truck bed liner.