This is a set of tools to check either a radius or a diameter. The hooked end has the labeled radius on the inner and outer edge. The round end has the labeled diameter hole and the labeled radius outer edge.
For example if the hooked end has a 5 printed on it, the inside curve has a radius of 5mm, the outside curve has a 5mm radius. If the end with a hole has a 10 printed on it, then the hole is 10mm diameter, and the outer edge is 10mm radius.

All have a 5mm hole in the center, and a small tick mark to identify the start/end of the curve. Gauges for both inch and metric: 1mm-26mm radius (1mm increments), and 1/16"-1" radius (1/16" increments).

Thank you for your input:
Mr. Smout: http://www.thingiverse.com/Smoutech/overview
asmacdo: http://www.thingiverse.com/asmacdo/overview