Middle Atlantic R4CN-4530B The R4CN-4530B R4 Series 30" Deep 45U Four-Post Open-Frame Rack with Cage-Nut Style Rails from Middle Atlantic is a heavy-duty rack designed to accommodate deeper and heavier components than traditional two-post open-frame racks. This unit is ideal for housing servers, networking equipment, routers, and switches, among many other possibilities. This model features cage-nut style rails. Its open design promotes airflow to ensure that your equipment stays cool and extends its useful life. The rack can also be ganged to additional four-post or two-post open-frame racks, making for virtually unlimited expansion possibilities.