Important: Before installing Mac Pro in a rack, read the safety notes found in
Insert the rear rail assembly’s pins into the back of the rack, then push the front of the assembly into the rack.
The rail should insert in the rack and the assembly should snap into place. If this doesn't happen, the rail may be locked. In this case, pull the orange lever on the rail to unlock it.
Repeat steps 1 to 3 for the other rail assembly.
Attach the inner rails to the sides of Mac Pro, making sure that release latches are towards the front of the computer and the rail eyelets are well placed onto the Mac Pro rail posts.