Epson EQUITY 3865X/20 PLUS - Manual (Page 161)

6. Pick up the hard disk drive and hold it so the mounting
plate is facing the subassembly, as shown below.
tabs
Notice that there are two tabs facing downward on the
bottom of the mounting plate. These tabs will fit into two
slots in the right side of the subassembly.
Installing and Removing Disk Drives
7-17