If you look carefully at HSD spindle pictures you can tell the difference between the shaft fans and the electric versions. Both have a square black top. The shaft version is about 1 1/4" above the case extrusion and is slightly rounded, made from plastic which has molded slots. The electric fan version is about 2" tall, rectangular with a bolted on fan grille. Picture Gerry linked to was a shaft fan model.
CNC Technology & Training
The Ultimate Woodworking Machine
GCnC411 (at) gmail.com