We think these were made for microfiche projection, but not certain. Beautiful brand new lens assembly in the original packaging! Barrel is 34mm long x 28mm OD with groove about 20mm from the front. Clearly made to go into some instrument and be held in place using the groove. Front element is 14mm diameter and back element is 10mm. Multi-element, with coated optics. Marked "Mag. 23X" Gloss black-enameled aluminum barrel. Makes a nice color corrected magnifier, but has a narrow field of view.