Not tractor related but this is on old cars. Decided to try a switch of rear bumpers as the one on the 53 Merc parts car looks better than the one on the "driver" 52 Merc. Some of the bolts came out ok but I've hit one that got so stubborn I had to use a "zip disk" to cut it off. 65 years of rust and corrosion. Can't get an air impact on it either. They are a bit overkill , 5/8 inch , fine thread bolts. Some of it in the video here.