Rack cabinets are hardware enclosures, typically centered around 19-inch wide frames, which organize, cool, and secure servers, networking equipment, and other IT hardware, as well as provide interconnectivity and cable management. Through the use of rails, shelves, drawers, and doors, a rack cabinet can be used to store and organize components such as servers, routers, switches, power and patch panels, firewall appliances, VoIP equipment, and other IT peripherals. The frames are usually made of steel and sized and/or bolted together to make a secure cabinet. They also provide ventilation and noise containment, as well as access and containment for cables. Rack cabinets come in various sizes and makes; the most common are 42U and 45U, though other sizes are available. They are also available in various depths, heights, and materials.