Acer Altos R920 Series - Manual (Page 178)

Appendix A: Rack mount configuration 160
5 Attach the CMA (cable management arm) to the rear of the server.
The CMA allows you to tie-wrap all cables to and from the system.
As you slide the system in and out of the rack, the CMA collapses
and extends, keeping the cables untangled and attached to the
system.
(1) Insert the smaller CMA extension into the rear of the left inner
rail (A1).
(2) Insert the larger CMA extension into the rear of left mounting
rail (A2).
(3) Insert the CMA extension connector into the rear of the right
mounting rail (B1).
(4) Insert the CMA arm connector into the blue plastic cutout on
the CMA extension connector (B2).
(5) Attach the cable clips into the appropriate mounting holes in
the CMA (C).