Patent ID: 7284672

Claim:
A multi-stage fastening structure, comprising: an extension rod having two screw holes formed on a lateral retaining plate at each end of the extension rod and a connection part mounted at each end of the extension rod near the lateral retaining plate; a plurality of locking devices, each having a first flange and a second flange having different outer diameters from each other; and two fastening devices, each comprising a sliding plate and a fastener, wherein the sliding plate comprises: a locking part formed by bending the sliding plate and being locked to the connection part; 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, and the fastener comprises: a slideway formed on each side for being coupled with the track; an inward retaining plate formed on one edge of the fastener; a fingerboard formed on the other edge of the fastener; and a locking pawl formed on the bottom of the fastener near the fingerboard, whereby when coupling the fastener with the sliding plate, the slideways of the fastener are slid along the tracks such that the locking devices can be coupled with connection holes with different apertures on a coupling plate by use of the first flanges or the second flanges, and that a locking position of the fastener on the sliding plate can be adjusted so as to couple the extension rod with the coupling plate.