Product review (5 stars): Great part, though you probably don't really need it
Yeah this is the part you are looking for if your center hole is reamed in a perfect circle and is now slipping on the shaft.  But your dryer is old and you want to get it working tonight since you finally took it apart.  Just redneck repair it and it will be good as new.  Just fashion a key with some wood or metal or whatever you have laying around, shove it in the hole as you put the fan back on the shaft, cut about a 1" section of rubber hose with a little bigger diameter than the shaft, slit the hose section, wrap it around  the shaft/plastic part of fan and secure it tightly to the shaft with a hose clamp that you can tighten with a screwdriver or socket.  This should keep your squirrel cage attached securely to the shaft for the rest of the life of your dryer.  But this is a great part if you can go without your dryer while you wait for this to show up.