Hi, I am Blair Haas, CEO of Bud Industries, and welcome to our Ask a Bud Expert series. One of the questions we are most often asked is, “can you explain the terms that we come across defining the dimensions of panel mounting rails and panel space in server racks?”

These terms are used on virtually all network and server racks globally. Panel rails are typically made of steel and are used to install and hold your 19-inch equipment such as servers. The hole pattern is standardized, and they are drilled on a pattern from hole to hole of 0.625 inches on 0.625 inches and 0.5 inches. That totals up to 1.75 inches, which is known as a “U.”

The U is a unit of measure of the vertical height of your equipment or panel height available in a server rack into which you can mount your equipment. So 40 U is 70 inches.

In this drawing the panel height is noted by the A dimension but note that the overall height is number B. The nominal panel width of most server racks is 19 inches. However there are three different dimensions of this width that you need to know.

  • From near edge to near edge… so the open space is 17.9737 inches.
  • From hole center to hole center is 18.312 inches.
  • And from the far edge to the far edge is actually greater than 19 inches at 19.125 which allows for the tolerance of both the rack and the equipment.

If you have any topics you would like us to address or more questions, please don’t hesitate to reach out.