Abstract: A fastening device is provided for securing of liners to the interior of pickup truck cargo beds. The fastening devices include a base plate which overlies the outer surface of a bed liner and a locking tongue projecting laterally from a bottom of the plate to extend through an aperture in the liner sidewall and to mechanically couple with a flange of the cargo bed sidewall to effect clamping of the liner to the flange. The locking tongue is formed with a peripheral edge surface that includes a locking surface angularly disposed with respect to the base plate forming in cooperation therewith for receiving edge portions of the liner and flange in clamped relationship, a camming surface that rides against an edge of the aperture in the liner during insertion to facilitate assembly and a locking surface that automatically engages the liner to maintain the fastening device in locking engagement.