Rack Installation Guide 1-21
Figure 1-14. 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 88 mm (3.5 inches) above the original mark you made (or count up six
holes in a rack with universal-hole spacing (see Figure 1-13).
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 0.625, 0.625, and 0.5 inches (see Figure 1-13).
NOTE: If your rack has universal-hole spacing, you have completed the procedure for
marking the rack.
3
Place a mark 88 mm (3.5 inches) above the original mark you made (or count up to the
fourth hole in the rack with wide-hole spacing (see Figure 1-14).
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 1-14).
44 mm (1.75 inches) (1 U)
12.7 mm (0.5 inch)
31.7 mm (1.25 inches)
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