This adapter allows using a camera (film or digital) with a microscope to take hi-res pictures of micro world.
Camera side mount is very common M42. There are many M42x1 adapters on the market, so you can find it for virtually any camera that allows it physically.
Dovetail part is made with 50.4 mm max diameter. This corresponds to optical connection of American Optics / Reichert Diastar microscope.
Very easy to use, and picture quality is very high.