Hengke metal shelving racks include four steel poles, usually consisting of 600 to 2200mmin height, unless you are going to buy a utility cart. With shelves that are 18, 24, 30, 36, 42, 48, 60, and 72 inches deep. Wire Shelves have openings and have four holes on the corners where the poles insert and little plastic clips connect the shelving together. The shelves are held on groves by the poles usually running every inch. Individual shelves can be put at any height and moved up and down when the unit is fully assembled without taking apart the unit or moving the other shelves.