Dell OptiPlex GX520 - Manual (Page 80)

3. Select the drive-panel insert in front of the drive bay that you want to use.
4. Gently press the release tab of the insert to remove it from the drive panel.
5. Reattach the drive panel to the front of the computer.
The drive panel only fits one way.
1 drive panel
2 release tab
3 drive-panel insert
1 CD/DVD-drive panel insert
2 floppy-drive panel insert
3 holder for shoulder screws