Acer Altos MU.R230E.001 - Manual (Page 140)

Appendix B: Rack mount configuration 130
Installing the cable arm option
The cable arm option allows you to tie-wrap all cables to and from the
system. As you slide the system in and out of the rack, the cable arm
collapses and extends, keeping the cables untangled and attached to
the system.
To install the cable arm:
1 Attach the cable arm to the rear panel using two U#6-32 x 6.4
screws.
2 Install two M6 cage nuts into the vertical rail to which the cable
arm is to be attached.