Front side - M28x0.75 female thread and M49x0.75 female thread
Rear side - M49x0.75 male thread
Weight - 20 g
This adapter allows using microscope objectives with M28x0.75 mount thread in front of lenses with M49x0.75 filter thread (for macrophotography purposes).
Front side has also M49x0.75 female thread, and you can use extra accessories like a circular light.