Good ole Stihl for some reason didn't feel it was neccessary to leave much of a "nut" on the clutch .You take a standard 6 point deep socket it was a chamfer build it on the business end and you have hell of a time to keep it on .
I have black iron industrial sockets by the 5 gallon buckets full,literally hundreds if not thousands .I doctored one up on a belt sander and that did the trick .With the help of a 1/2" breaker bar and a 3 foot pipe cheater of course .> impact wrench .