Dell Precision Workstation 370 User's & Service Manual page 68

1 bracket within slot
2 bracket caught outside of slot
3 fully seated card
4 not fully seated card
7. 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.
8. Press the retention arm into place, securing the card(s) in the computer.