This is a lens pair that is cut from a large diameter optically ground glass single lens just like the classic stereoscope lenses were.  ~200mm focal length, these can be used for replacing the plastic lenses in the stereoscopes we offer or in replacing lenses in vintage stereoscopes (some modification of the stereoscope may be needed).  They can also be used by craftsman in making your own stereoscope. They are 1 1/4" square (35mm x 35mm, 11mm thick) and are wedge shaped just like the vintage lenses.  Add them to your stereoscope, with the thin part of the lenses towards the center, and the flat side of the lenses towards your eyes and you will have high quality viewing.