Vertical Hole Spacing: 1U equals 1. 1 mm) from the top or bottom of the U. Holes are grouped in sets of three, with each group representing one Rack Unit, commonly called 1U. The spacing is measured center-hole to center-hole and remains consistent whether the rack has square or round mounting holes. For the front and back vertical rails, the center-to-center hole. The TPS 1U Chassis (Art. BJ9900001) is a standard 19-inch rack mount power supply chassis designed for industrial applications, also known as the TPS 1U Chassis, BJ9900001, 19 inch 1U Chassis, Power Supply Chassis, Rack Mount Chassis, Industrial Chassis, Electronics Enclosure, Server Rack. To allow space between adjacent rack-mounted components, a panel is inch (0. If n is number of rack units, the ideal formula for panel height is h =. Standardization in rackmount systems is essential for ensuring equipment compatibility, optimal space utilization, and global product interoperability. These issues are reviewed below.