I'm not sure if I can put this question in the lenses-department, but here it goes;
Lot's of digital camera's need an adaptor before you can put on lenses. It's logical that you need a 37 mm adaptor for a 37 mm lens.
What I don't get though, is how you know what adaptor fits on your camera. I assume the camera's themselves do not all have the same size of threads.
If I wanted to order from a catalog, how do I know which adaptor fits on the camera I (could) have?