The STC21 comes w/ a flat top shelf for added clearance. It also includes a bottom tub shelf for security and stability. The unit becomes mobile w/ 4 casters, two of which come w/ a locking brake to keep the cart firmly in place. Overall dimensions are 24w x 18d x 36h. Shelf Clearance is 26h. tub Shelves are 2 3/4d.