I have used a SAR RAT (4") blade and a Ratweiler (8") blade. I usually use the Ratweiler and have batoned at least 2 cords of wood. THe largest diameter is about 28". Not all at once, you have to shave it piece by piece but you can get through it. As for the grind, it depends on what your doing. I have never worked with a flat grind though.