Middle Atlantic R412-4524B The R412-4524B R4 Series 24" Deep 45U Four-Post Open-Frame Rack from Middle Atlantic is a heavy-duty rack designed to accommodate deeper heavier components than two-post open-frame racks. This unit is ideal for servers, networking equipment, routers, and switches, among many other possibilities. This model features 3/16 inches thick extruded aluminum rails with 12-24 threads. The rack frame is made of 16-gauge steel. Its open design promotes airflow and ensures that your equipment stays cool, thereby prolonging its useful life. The rack can also be ganged to additional four-post or two-post open-frame racks, making for virtually unlimited expansion