American Power Conversion AP7902 AP7911 - Manual (Page 9)

How to Install the Rack PDU
Switched Rack PDU Installation and Quick Start 5
For a recessed placement: use four flat-head screws (provided)
through the last four holes of each bracket.
2. Insert caged nuts (provided with the rack) on the vertical mounting
rails above a number at the start of two U-spaces in your enclosure
and below a number at the lower end of those two U–spaces.
3. Align the mounting holes on the brackets with the caged nuts you
installed in step 2, and insert four mounting screws (provided with
the rack) to secure the brackets to the enclosure.
2U