Acer AR380 F1 - Manual (Page 158)

Appendix B: 140
3 Attach the inner rails to both sides of the server.
a Align the holes on the left and right inner rails to the hooks on the
left and right sides of the server.
b Slide the inner rails to the front until the rails lock into place with an
audible click.
4 Install the mounting rails to the rack posts.
a Align and insert the tabs and latches on the left and right mounting
rails to the front and rear rack post mounting holes (1). Make certain
the proper mounting holes on rack post are selected.