Patent attributes
A multi-stage fastening structure comprises an extension rod, a plurality of locking devices, and two fastening devices. A lateral retaining plate is formed at each end of the extension rod. A first flange and a second flange having different outer diameters from each other are formed on each of the locking devices. Each of the fastening devices comprises a sliding plate and a fastener. The sliding plate comprises: a locking part formed by bending the sliding plate; a trench formed on the sliding plate; a track mounted on each side of the trench; and a plurality of through holes formed on the sliding plate in front of the trench. The fastener comprises: a slideway on each side; an inward retaining plate on one edge of the fastener; a fingerboard on the other edge of the fastener; and a locking pawl formed on the bottom of the fastener near the fingerboard.
