Remembering the sprocket/clutch nut on my Stihls are LEFT handed threads, I also use an impact gun to loosen the nuts. (Leave the spark plug in place)
*** HOWEVER *** Do NOT use an impact gun to tighten the nut when you put it back on. Many are made from aluminum and will strip out. (This was a safety feature to help the uninformed about left hand threads, from messing up the piston or threads on the crank shft while using a piston stop.)
If you tighten the nut to where it overcomes the compression of the engine, it will be tight enough. Using this as my reference, I have never stripped a nut. (I am sure there is a proper torque to use, but I couldn't tell you what it is.)
