Asus P5B Deluxe/WiFi-AP - Manual (Page 38)

-1 Chapter 2: Hardware information
5. Rotate each fastener clockwise to ensure correct orientation when
reinstalling.
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.
The narrow end of the
groove should point
outward after resetting.
(The photo shows the
groove shaded for
emphasis.)