3Com CoreBuilder 9000 Quick Installation Manual page 9

Figure 6 shows two types of racks that you can use.
Figure 6 Rack Types
Bolt the rack to the floor.
Brace the top of the rack against the wall.
Make certain that the rack is properly aligned and squared. Use a
framing square to ensure that the rack is squared.
If you install more than one chassis in a rack, install the bottom
chassis first. Make certain that there is sufficient space between
the bottom chassis and the top chassis.
7-Slot Chassis Quick Installation Guide 9