Middle Atlantic R412-5130B The R412-5130B R4 Series 30" Deep 51U 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 possibilities. The rack may be configured with the base on the inside to save rack space, or on the outside for increased stability. This unit will also accept 6, 9, or 12 inches cable ladders.