These are neat small multi element lens assemblies which when looking thru one end will produce a wide field image if used with an objective. 10mm focal length. Only 47mm long bu 19mm diameter at the large end and 12mm at the small end. All of them have some defect or cleaning needed internally. Not a clue what these were made for but some of the elements come out easily as one section unscrews to get at the elements. Several elements. Take it apart and use the good ones for your projects, or maybe you can find a use for it as is. Only have a few.