There are disclosed three embodiments of a fastener, a method of using a fastener, and a fragmentary portion of a mold. The fastener has a socket and a head joined by a flexible filament. The socket has a disc-shaped body, a transverse opening through the body, projections extending into the opening, and a post joined to each projection. The posts extend into the space within a side wall of the opening. The projections flex when the head is inserted through the opening, but the posts prevent attempted withdrawal of the head through the opening thereby preventing uncoupling of the head from the socket. The projections are so close that when the head is inserted into the socket, some of the plastics polymeric material of the projections deforms permanently, thereby work hardening the projections at the deformation. One of the fasteners has a head, a pair of relatively rigid sockets, a flexible hinge connecting the sockets to each other, and a flexible filament connecting the head and the pair of sockets. The one socket nests in the other socket when the sockets are moved to a position in which the socket openings are aligned. According to the method of use, the socket openings are moved generally into alignment and the head is inserted through both socket openings.