A floor jack and a frame therefor including a pair of arched side plates, hubs, axles, and spreader bars are provided. A first pair and a second pair of hubs are positioned at front ends and rear ends of the arched side plates respectively. A first axle and a second axle connect the arched side plates to the first pair and the second pair of hubs at the front ends and the rear ends of the arched side plates, respectively, using pairs of adjustable collars that pivot between lower and upper positions. The spreader bars separate the arched side plates along their length. The frame is configured for use in a conventional jack or in a mega jack to provide increased elevation by fixing the axles to the lower or upper positions of the adjustable collars. A frame is also provided for a fixed height floor jack including non-adjustable collars.