Epson 3865X Plus User Manual page 207

Make sure the holes fit over all the pins and then push the
connector onto the pins.
4. Pick up the hard disk drive and hold it above the vertical
mounting area so the mounting plate is facing the
subassembly, as shown below.
Notice that there are two tabs facing downward on the
bottom of the mounting plate. These tabs fit into two slots
in the right side of the subassembly when you install the
drive.
B-l6 Installing and Removing Disk Drives