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 have middle leg supports and casters for added stability, with six casters (three locking). Inside bottom dimensions of tapered standard drawer: 13a"l x 9a"w x 2½"h. Inside bottom dimensions of tapered deep drawer: 13s"l x 9¾"w x 5"h. Inside bottom dimensions of tapered wide drawer: 12a"l x 12a"w x 3½"h.