Dell OptiPlex 360 (Late 2008) - Manual (Page 39)

Cards 39
NOTE: If you are installing a PCI Express x16 card, ensure that the securing
tab on the connector’s release lever fits into the notch on the front end of the
card.
8 To secure the cards, gently rotate the release lever downward to move the
card retention latch into place.
1 card fully seated 2 card not fully seated
3 improperly seated bracket 4 properly seated bracket
1
2
3
4