Asus Motherboard P5LD2 - Manual (Page 34)

2-12 Chapter 2: Hardware information
5. Rotate each fastener clockwise
to ensure correct orientation
when reinstalling.
The narrow end of the
groove should point
outward after resetting.
(The photo shows the
groove shaded for
emphasis.)
Narrow end of the groove
Refer to the documentation in the boxed or stand-alone CPU fan package
for detailed information on CPU fan installation.