Tyan Computer GX21 - Manual (Page 23)

2.2 Rack Mounting
Chapter 2: Setting Up 15
Note: When fully extended, the sliding rails
will lock. The release mechanism is located
on the sliding rail as shown. Press the
release mechanism while pushing the sliding
rails to shorten them.
6. With the rails in their shortest condition, adjust both front
mounting brackets so that they are flush with the front of
the unit.
7. Accurately measure the depth of your rack and adjust the
rear brackets accordingly.
8. When all brackets are positioned correctly, tighten them.