The taper is larger on the long shaft models. The flywheel will go on the shaft but will go too far onto the shaft. A new flywheel costs too much. It's cheaper to find a short shaft Ryobi or one of it's siblings that doesn't run to strip for a flywheel.

Long shafts are 3/8" dia. Short shafts are 5/16" diameter.

Enjoy,

Jim