I just put a roll of Rollei Superpan 200 in my new-to-me Olympus OM-1 and I have a roll of Ektar 100 to finish up in my Pentax KX. It's fun to mix up the camera/film combination until I settle on the best combination. There are a few others waiting their turn.
So, if I am understanding this correctly, the flat part should not be flush with the camera body (see pic). It was screwed on backwards? If it is screwed in place it's pretty tight. I'll need to grab it with a needle nose plier to turn it.
I saw an old thread that came close to this issue. I have an FM2 and I would like a rubber eyecup for it. I purchased the DK-3 but cannot get it to install. Further inspection shows there is no ridge on the camera to fit into the slot on the eyecup (please excuse the overly technical language :-) ). See the attached pictures please and give me some advice if you can. Any help will be greatly appreciated. I'm certain that I am missing something.