Apple Xserve (Early 2009) - Manual (Page 15)

15 Chapter 1 Installing the Xserve
 If you have a threaded-hole rack, start with the rail flanges outside the rack posts and
compress the rail into position.
Position the spacer
over the threaded guide
on the rail assembly.
This end is up.
Compress the rails
so that they fit on the
outside of the rack posts.
Use either eight 10-32 or eight
M5 screws (supplied), depending on
which type your rack requires.
2 Slide a spacer, with the arrow up, over the small round guide at the ends of each rail
and install the mounting screws finger tight.
Don’t tighten the mounting screws until you align the rails in the next step.