A fastener (10) for locking receipt in an opening (34) of panel (36) has an upper end portion (16), a flange (18), and a locking insert (24) for receipt in the opening (34) and forcibly distended to prevent removal of the fastener from the opening. A number of gripping means (22) formed in a surface of the flange (18) each include a knifelike edge (32) with a slot (33) at each side thereof. The gripping means bite into the panel providing purchase resisting rotation of the fastener relative to the panel.