This is an adapter which can be threaded onto the front of a lens with a 52mm filter size.
photo in the kitchen to test
another view for a quick test
Here is the caption from a listing for another adapter
Offered for your consideration is this remarkable Miida Universal Stereo Adapter Model SA-1 made by Marubeni-Iida, circa 1971. It is almost identical in appearance to a famous brand of Stereo Adapter that is now highly sought-after by many stereographers around the world. The female threaded screw mount is designed to fit any lens with 52mm male threads. Ring adapters may accomodate some other sizes (a 55mm adapter is included). It is designed for use with 35mm film SLR cameras only! Any other use would be strictly for experimental purposes.According to the instructions, the Miida Universal Stereo Adapter is supposed to work with any lens, provided the focal length is from 55-300mm. However, I never had any luck using it with my standard issue 58mm lens. (Perhaps the acceptance angle of my lens is too wide?) Since I'm primarily interested in stereo photography, I never got a different lens for my SLR just so this SA-1 would work with it. I use my "real" stereo cameras, instead. For all I know, the Miida Universal Stereo Adapter may need to be adjusted (internally) by a professional or someone who has the know-how to do that.