This is an Aimpoint Micro S-1 with a 6MOA dot. It's designed to mount on the rib with carbon fiber plates. By switching plates, it'll install on ribs between 6mm and 12mm. It mounts really low. This was purchased last year for my son's turkey gun. So, it's been used one season. I see no flaws in the glass. He and I both really like it. However, we built new turkey guns last fall and went with a receiver mount. Those carbon fiber plates worked as advertised in that they didn't mar the rib in any way. I'm about half-tempted to keep it, but thought I'd offer it here. I'll take $500 shipped CONUS. Payment by PayPal.