Asus KGPE-D16 - Manual (Page 34)

2-14 Chapter 2: Hardware information
2. Attach one end of the retention
bracket to the retention module
base.
3. Align the other end of the retention
bracket to the retention module
base. A clicking sound denotes that
the retention bracket is in place.
4. Push down the retention bracket
lock on the retention mechanism to
secure the heatsink and fan to the
module base.
Ensure that the fan and heatsink
assembly perfectly fits the
retention mechanism module
base, otherwise you cannot snap
the retention bracket in place.