There is disclosed a one-piece molded fastener composed of plastics material, wherein there is a socket hav ing a through-passage and a head connected by a filament. The head is insertable into the socket in one direction to be non-releaseably gripped by prongs or spring fingers on the inside of the socket. There is a provision on the head for preventing the head from being inserted into the passage through the other end of the socket to a position where it would be releasably gripped by the prongs.