MSI X99A SLI PLUS Manual page 26

5. Line up the CPU to fit the CPU socket. Be sure to hold the CPU by the base with
the metal contacts facing downward. The alignment keys on the CPU will line up
with the edges of the CPU socket to ensure a correct fit.
6. Carefully close the load plate and remove the plastic protective cap.
7. Close the active lever with a smooth uniform motion and latch to the socket.
8. Close the hinge lever with a smooth uniform motion and latch to the socket.
Alignment Key
En-12