I have to measure a .04"(1mm) wide groove that is very close to a bottom surface.

This could be verified easily with a size gage and radius gage but THE BOSS wants CMM numbers.

The smallest disc probe that I could find is 1.2mm (about 2mm) with rollers

I was also thinking using a star assembly with .3mm ball but the bottom screw will hit the surface first.

Any suggestions from you guys will be greatly appreciated. Thank you!