Users Guide

Two-Post Rack Installation 31
Wide-Hole Spacing Racks
Racks with wide-hole spacing have an alternating pattern of two holes per rack unit with center-to-center
hole 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 Spacing
To 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 are
installing 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 rack
with 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 holes
with 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 in
the 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 with
center-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)