[BJC]

First off, Aren Hill deserves all credit for this idea.

Basically, the mounting holes for a CIM type motor are the only access points to the inside of the motor. For reasons described earlier cooling is much more effective when air is forced directly past the armature. When you put 2 and 2 together you end up with hollow fasteners. I'll leave the rest as an exercise to the reader.

Cheers, Bryan