Blue Hills Studio Storage Carts feature a 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 a total of six casters (three locking).