Flywheel nut
Yep! Sears has one for like 38 bucks.... 20 bucks if you find it on sale... Then, get a big breaker bar.... when you are done with that...click the f-ing search button.... should come right off.
Took me awhile to find a 54 mm in my area. I finally found one without spending too much but it wasn't an impact socket. It did however hold up to the 300 + ft lbs of pressure it took to get that thing off.




