Leica 0.5x objective lens for M3Z and other similar Leica microscopes. The outer casing has a small imperfection that does not affect it's use or clarity. The groove was used to attach another device for testing only, then removed. No scratches, dings or dents. Lens id perfect. The threads are not crossed and mounts without any issues. Binoculars and eyepieces for Leica microscopes are also available. See my other items. Over 40 years' experience.