Anyone Know how to take these mirrors apart?

Just bought some JDM mirrors came off an Eunos NA. They look well made only I can't seem to find a way to take them apart. There are no screw on the outside and I have tried twisting the rings off with an oil filter strap but ti would not move. They do pry up a little though maybe 1mm. Don't want to destroy them as I need to dismantle them to get them Xylan Coated.
Does anyone have any experience with these please?