If you are installing the router in a center-mount open-frame rack, you must first install the large mounting shelf on the rack. The spacer bars are not needed for this mounting option; however, you can leave them attached to the front-mounting flanges.
Open-Frame Rack Mounting Hole Locations specifies the holes in which you insert screws to install the mounting hardware in an open-frame rack (an X indicates a mounting hole location). The hole distances are relative to one of the standard U divisions on the rack. For reference, the bottom of all mounting shelves is at 0.04 in. (0.02 U) above a U division.
To install the large mounting shelf (see Installing the Mounting Hardware for an Open-Frame Rack):