This is a differential adjuster micrometer head. From the information that i have it has a 7 mm travel. The units and resolution are metric.
This was used in optic adjustment and tuning.
This is old inventory but all parts are new and in boxes
The one in the picture is only for display purposes as I removed it from the box and I also ran the full travel so I don't won't to sell this one. But all the others are still in the box and plastic bag.