Many people have found success with their shoe. Use the bottom of a good rubber bottom shoe, press down hard and twist. Some mouse pads may also work for this.
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Snap ring pliers is what I have used. Make sure the tips are long enough to reach in to engage the small notches and it might help to heat up the area with a hair dryer first. Be careful not to slip out of the notches or you will likely chew up the threading.
I also recall reading a post by a member that used a saw blade trimmed down to fit inside the head as a good solution as well.