I put my 6PD bezel in my padded vise and used a soft thick towel to lay over top of bezel.
I used a piece of brass about 3/8" in diameter to lay over the rag and between the deepest part of the crenellations, push down hard so not to slip and turn CCW, came off after a few tries with no scratches or mars on my bezel, it worked fine. :thumbsup:
It should work for the M6 too.