All steel wire tubing construction. 3-Shelf unit includes (1) top / (1) bottom / (1) middle shelf. 4-Shelf unit includes (1) top / (1) bottom / (2) middle shelves. Front door has top flange and lockable handle. Includes two 5” swivel casters and two 5” brake casters. Also comes with bumpers. See page 763 of our 2011 catalog.