This is the piece that holds 
the fan blades to the shaft 
that is coming from the motor. 
The are made of very heavy 
Brass or Bronze. You don't 
always need this, but when 
you do, nothing else will work. 
Its best to get some of these 
parts for the older Incubators 
and Hatchers, while they 
are still available. They will 
not always be available.