Abstract: A fastener assembly for attaching a truck bed liner to a truck body, is described, which includes a support member, having a face plate and a trough-shaped wall, for supporting a linearly movable clamp member. The clamp member can be rotated within the trough, in order to swing a clamp arm upwardly to a generally vertical position, aligned with a downward lip, on a truck rail. A manual screw extends within the trough into a threaded hole in the clamp member, such that the screw can be rotated, to rotate the clamp arm, and then move it linearly along the trough, and into clamping engagement with the rail lip. The fastener assembly is a self-contained unitary structure, that can be installed through a circular opening in the bed liner side wall, after the liner is placed in position within the truck bed.