It is a device that uses a pin and the pressure that it exerts on a surface of a sample to measure the sample's thickness (usually in units of micrometers). For example, if you wanted to find the thickness (in micrometers) of a sample of metal. You could place the mount/stand in the microcaliper and take the measurement. Then, measure the mount/stand with the sample. The difference between the two measurements will be the thickness of the sample.