Abstract: A chain guard fastener for secure fitting of the down tube and the seat tube of a bicycle comprises a fastening means and bolt having a key projecting in front thereof to permit engagement with a counterpart keyway provided on the chain guard. The fastening means is made of molded plastic, and includes a median split and a cylindrical form projecting out of a pair of symmetrically disposed faces, two suitably formed bolting ports traversing the pair of faces on either side thereof so as to permit passage of a bolt therethrough. One end of the bolt is stopped, while the other end of the bolt goes to a continuously toothed groove, in close proximity of the teeth.