use a block of wood to lock up the blade from turning. I wedge it against a bolt or bump out or lay the mower on its side and step on the board to hold it. Torque values are normally a range. Use the lower range if you cleaned and oiled the bolt, or the higher if it is dry. Most manufacturers will send a new oiled bolt if you order a part from them, so the factory is often using an oiled bolt on assembly. When I say oiled, I mean lightly glistening and not wet with oil.