The present invention provides a supporting rack, one lateral end thereof is provided with a connecting section and the base thereof is provided with an extending section, at least one clamping ring is formed at the free end of the extending section and an opening is provided between the clamping ring and the extending section; an auxiliary connecting member used to connect a reinforcing sheet to the extending section, a positioning sheet is formed by vertically bending one end of the reinforcing sheet and is formed as one piece with the reinforcing sheet; a core hole is axially provided on the positioning sheet, with respect to a location of a shaft hole of the clamping ring and with respect to a size of a shaft rod; a pivotal shaft, the shaft rod is axially extended from the pivotal shaft; the shaft rod passes through the core hole of the positioning sheet and is tightly connected thereon, and is covered by at least one clamping ring.