Square rack holes are the most common rack holes in the market today. The standard square sizes are 3/8” by 3/8” varying from 1. This guide dives into the practical aspects of server rack design, including the types of screws, rails, and enclosures. Before installing system components, locate the hole pattern in the rack rails to allow adequate Unit height (U) of vertical space. Rack cabinets that meet EIA-310 standards have an alternating pattern of three holes per rack unit. For the front and back vertical rails, the center-to-center hole. M6 Cage Nuts, Screws and Washers [Size: M6 x 16mm 50 Pack] Rack Mount Screws Hardware for use with Network and Server Rack Accessories, Routers, Cabinets and Enclosures. Discover reliable rack mount cage nuts designed for square-hole racks.