Unique patented interlocking rail and drawer system that prevents shifting off the rails. Molded stops on drawers prevent drawer from pushing through the back of cart. Each drawer can hold up to 3 lbs. Carts have four casters (two locking). Double-wide-carts (12-drawer and-20 drawer units) have middle leg supports and casters for added stability, with six casters (two locking). Inside bottom dimensions of atpered standard drawer: 13 3/8"l x 9 3/8"w x 2 ½"h. Inside dimensions of tapered deep drawer (3-drawer and 6-drawer units): 13 5/8"l x 3 ¾"w x 5"h.