Dell DSS 2500 Owner's Manual page 61

Steps
1 Align the tabs on the cooling shroud with the securing holes at the back of the chassis.
2 Lower the cooling shroud into the chassis until it is firmly seated.
Figure 15. Installing the cooling shroud (135 W processor)
1 cooling shroud
3 cooling shroud alignment pin (2)
Figure 16. Installing the cooling shroud (140 W processor)
1 cooling shroud
Next steps
1 Install the optional PCIe expansion card riser.
2 If disconnected, reconnect the cables to the expansion card(s).
3 If required, open the expansion-card latch on the cooling shroud to support the full length expansion card.
4 Follow the procedure listed in the After working inside your system section.
2 cooling shroud alignment slot (2)
Installing and removing system components 61