Up for sale is a vintage Leitz Wetzlar Stereoly stereo attachment, serial #1278, which unfortunately does not include the mounting arm & finder so it is not really usable in its current state (it fits smoothly onto a 5cm/3.5 collapsible Elmar as shown in the final photo, but without that piece of foam underneath it, it would just fall right off since it doesn't have the mounting arm holding it to the camera body).  Also be sure to note that the optics contain internal haze and fungus, and they would benefit from a professional dismantling and internal cleaning.  Cosmetically, there is moderate overall wear to the attachment, including some scratches and paint loss which is most prevalent at the edges and corners.  Obviously, the camera and lens shown are not included with purchase but are shown for scale.  Please be sure to fully enlarge the provided photos, and feel free to contact me with any questions you may have.