Rogowski coil current probe, FreeCAD parametrized

A Rogowski coil is used to measure the current in a wire through the center of the coil. See for details for example:
https://en.wikipedia.org/wiki/Rogowski_coil

The FreeCad script generates the body of a Rogowski coil with specified dimensions and windings etc. The gap in of the coil makes it possible to easily slide the coil over a current carrying wire (shown in gray on the first figure in the gallery)..

The windings on the coil are guided by small channels and there are two holes in