20E609 up for sale is a new aluminum 10 blade fan this has a od of 4 1/2 (actual size just under 41/2 at 4.470 ) inches diameter the inner hub has a 3/16 (0.187  ) inch inner diameter and has a set screw to mount this to the rotating shaft , the hub is about 3/8 long (0.400) long the fan is about 1 inches wide, nice fan for many cooling applications or special projects or to replace a broken one , this is a new fan but might have some minor bends from storage , comes as shown on photos, the center hub is made from aluminum too and has a small steel set screw to hold it on to the shaft , this hub has a OD of 0.564 inch x about 3/8 wide total over front of hub  to back of fan, blade is all aluminum but the small set screw is steel , 

details from manufacturers web page 

300 cfm @0.000-IN SP

CW facing discharge 

30 deg pitch

max rpm 3000 

width 3/4 inch