MSI MS-6111 Manual page 14

Step 1: Place the bubble bag that came with your mainboard or use
any soft material like Styrofoam underneath the mainboard. Find a
flat surface to do the installation.
Step 2: Install the Retention Mechanism.
Look for the key on Slot 1, and match it with the Notch Key on the
Retention Mechanism for the proper direction. Then, insert the Two
Keylock of the Retention Mechanism into the two holes on the sides
of Slot 1. Take note that one hole is wider than the other. The
Retention Mechanism will only fit in one direction.
Notch
Key
Keylock
(Wider)
SLOT1
Key
Push the Retention Mechanism onto the mainboard, until you hear a
"click" sound. Check for a perfect fit.
Retention
Mechanism
2-4
Keylock