Oracle X9-2 Owner's Manual page 42

Install the front cage nuts.
5.
Caution:
Installing the storage shelf without the front cage nuts will cause the storage
shelf to be unstable. You would then need to remove the storage shelf from the
rack to install the cage nuts.
The following figure shows how to install the front cage nuts in the rack:
Chapter 4
Installing the System Into a Rack
4-15