The blade nut takes a 15/16 socket. Lay the mower on it's side (empty fuel tank) Use a breaker bar with socket and either rap it with a mallet or hold the blade with a glove on or a use a rag and loosen the nut by arm strength. (of course if you have an impact wrench available...) Blade nut should be torqued with a torque wrench. Normally to about 525 inch pounds.