Dell OptiPlex GX260 Series System User's Manual page 158

1 bracket within slot
2 bracket caught outside of slot
3 fully seated card
4 not fully seated card
11. Before you lower the retention arm, ensure that:
The tops of all cards and filler brackets are flush with the alignment bar.
The notch in the top of the card or filler bracket fits around the alignment guide.
Press the arm into place, securing the card(s) in the computer.
Closing the Retention Arm