Two-Post Rack Installation 31Wide-Hole Spacing RacksRacks with wide-hole spacing have an alternating pattern of two holes per rack unit with center-to-centerhole spacing (beginning at the top hole of a 1-U space) of 31.7 mm and 12.7 mm (1.25 inches and 0.5 inch)for the front and back vertical columns of holes (see Figure 2-3).Figure 2-3. Two-Post, Open-Frame Relay Rack Wide-Hole SpacingTo mark the rack, perform the following steps:1 Place a mark on the rack's front vertical rails where you want to locate the bottom of the system you areinstalling in the two-post rack.The bottom of each 1-U space is at the middle of the narrowest metal area between holes.NOTE: If your rack has wide-hole spacing, go to step 3.2 Place a mark 44 mm (1.75 inches) above the original mark you made (or count up three holes in a rackwith universal-hole spacing) (see Figure 2-2).Each 1 U (44 mm, or 1.75 inches) of vertical space on a rack with universal-hole spacing has three holeswith center-to-center spacing between holes (beginning at the top of a 1-U space) of 15.9 mm,15.9 mm, and 12.7 mm (0.625 inch, 0.625 inch, and 0.5 inch) (see Figure 2-2).NOTE: If your rack has universal-hole spacing, you have completed the procedure for marking the rack.3 Place a mark 44 mm (1.75 inches) above the original mark you made (or count up to the next hole inthe rack with wide-hole spacing (see Figure 2-3).Each 1 U (44 mm, or 1.75 inches) of vertical space on a rack with wide-hole spacing has two holes withcenter-to-center spacing between holes (beginning at the top of a 1-U space) of 31.7 mm (1.25 inches)(see Figure 2-3).1 U (44 mm or 1.75 inches)12.7 mm (0.5 inch)31.7 mm (1.25 inches)
