Dell OptiPlex 960 (Late 2008) - Manual (Page 9)

6. Place the card in the connector and press down firmly. Using the following illustration as a guide, ensure that the card is fully seated in the slot.
7. Gently rotate the release tab downward to move the card-retention latch into place to secure the cards.
1 PCIe x16 card 2 release lever
3 securing slot (not all cards) 4 securing tab
5 PCIe x16 card connector
1 card fully seated 2 card not fully seated
3 bracket within slot 4 bracket caught outside of slot
NOTE: If you are installing a PCIe x16 card, ensure that the securing tab on the connector's release lever fits into the slot on the front end of the
card.
1 release tab 2 card-retention latch
3 card 4 card-edge connector
5 card connector