Acer Altos R520 M2 Series User Manual page 167

3 Install the mounting rails to the rack posts.
Determine the vertical position in the rack. Refer to "Vertical
mounting hole pattern" on page 146 for more information.
(1) Align and insert the mounting rails into the front rack post
mounting holes. Make certain the proper mounting holes on
rack post are selected.
(2) Use two metal screws supplied with the kit to secure one end
of the mounting rail to the rack.
(3) Align and insert the mounting rails into the rear rack post
mounting holes.
(4) Use two metal screws to secure the other end of the mounting
rail to the rack.
(5) Do the same thing to the other mounting rail.
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