In trying to model cast parts, the inside radius of curvature is often hard to measure with just calipers. The STL files are stepped half-rods that start with 10mm diameter and 20mm diameter. Select the step that best fits the curve in your casting, then read or measure the diameter/radius for your modeling software. These can also be used for karge hole measurement in locations that a ruler or calipers are difficult. SCAD source files are included. Adjust parameters for minimum diameter and number of steps. Step size is 2 mm diameter or 1 mm radius. Diameter is marked on alternate steps in the flat surface, also.