the standard blade nut torque is 80 ft/lb when you add grass clipping and rust i have had to heat the nut with a cutting torch and then remove nut with a 450 ft lb impact wrench because my 250 still wouldn't touch it. the blade sits on a star mount and will not twist if hit with a hammer. i don't even try my 250 impact wrench on mtd blades anymore because it is not bid enough to remove the nuts from those decks. most mtd blade nuts are 15/16 not 1 inch. you can also try wire brushing the nut and the exposed thread area at the bottom of the nut. that my help.