The most common rack width is 19 inches on the inside. This follows the EIA-310 standard, which defines the mounting space between the vertical rails. Nearly all rack-mounted equipment—servers, switches, patch panels—is built to fit this standard 19” width. 5″) to allow space for cable management and airflow. Options include 24″, 36″, 42″, 48″, and 59″. Choose between 2-post (for. This section includes the specifications for constructing and building out of Telecommunications Equipment Rooms (MDF/IDFs) to be used for supporting telecommunications and other special systems. Understanding the. design.