Luddite Frank
Well-known
I did not unscrew the ring, I just tucked the disc of gel into the channel between the glass and the bezel with a round, pointed wooden toothpick.
It was a little bit fiddly, but turned-out well.
If you really need to remove the ring, a clamp-type wrench is the "official" tool; a rubber jar-lid gripper might give enough grip on the knurling under finger pressure.
