This is to be used on older Obsessions prior to when this became standard. These are new and unused. Per Obsessions web site...
NEW SECONDARY MIRROR HOLDER
Spring action push-pull adjusting secondary mirror holder. Our new design makes collimating the secondary mirror easier than anything on the market. No screwdriver needed. No need to loosen an opposing screw to tighten another like on 4 screw designs. No fumbling around in the dark. Three brass knurled knobs with compression springs allow you to collimate the tilt of the mirror without even looking at it. Takes only seconds to do. Now the best is even better.