A clip assembly for gripping a sheet of material. The assembly includes first and second jaw members having ramp portions which are joined along a common hinge. The ramp portions form divergent inclined planes, and are surrounded by a sliding collar. As the sliding collar is moved from the hinge area toward the grip portions of the jaws, the latter are forced together against the sheet of material. A releasable ratchet pawl locks the sliding collar against reverse movement. The clip assembly is suitable for fabrication from injection molded plastic.