Epson 3865X Plus - Manual (Page 239)

There are four corresponding tabs on the inside back panel
of the computer which fit into the openings in the
subassembly slots.
tabs
Lift up the subassembly from your work surface and lower
the back end into the computer, fitting the top tabs in the
computer into the openings in the top slots on the
subassembly, as shown in the next illustration.
B-48 Installing
and Removing Disk Drives