Epson Equity 320SX PLUS - Manual (Page 94)

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, guiding the top
slots on the subassembly into the top tabs on the
computer.
5-10 Accessing Internal Components