Asus Motherboard P5ND2 - Manual (Page 27)

ASUS P5ND2 1-15
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.