The official Leica name is Reflector Holder. These are tools that measure a feature, like a circle, that is smaller than the diameter of a corner cube reflector. The top is magnetic, and it sticks to a 1.5” Corner Cube Reflector (CCR).
Leica Reflector Holder
You make measurements by placing the pin nest probe into the circle and then taking hits with the pin following the inside diameter (ID) of the circle.
When you measure a hole or an internal slot with a reflector attached to a pin nest probe, be sure to lift the probe away from the center of the internal feature when you finish creating or measuring the feature. This way, PC-DMIS properly calculates the vectors. Otherwise, the feature's vector may be reversed.