Epson EQUITY 386/33 PLUS - Manual (Page 99)

Then place the flat side of the mounting plate on the hard disk
drive and align the four holes on the plate with the four
holes on the drive, as shown below.
mounting plate holes
3. Use the four screws that came in your hard disk drive kit to
secure the mounting plate to the drive.
Installing the Drive
If you are going to install or remove a drive in one of the
horizontal drive bays, first follow the instructions under
“Installing or Removing a Drive in the Horizontal Position” on
page 5-19. Do not install the vertically mounted drive until you
finish installing or removing any horizontal drives.
Installing and Removing Drives 5-11