Fillet / Round Measuring Adapter ! Important conversion factor!

This tool is meant to be used with your vernier calipers extension thingie (see picture) .

Radius = Caliper Reading x 2.414

Extend the limits of your caliper.

This tool can also be used to extend the reach of your caliper.
For example, my caliper has a maximum reading of 150mm. But this tool allows it to measure object diameters upto 724mm. (This is because of the multiplication factor above).

Max.Radius Reading = Max.Caliper Reading X 2.414

Design

I did some quick geometric calculations to get a relationship between caliper length and radius. Then verified it on CAD. Printed out a test piece and verified that with some real life measurements.