* BoltFactory was written with 1mm Blender Units in mind (Blender
units are now officially 1m)
* Addon already suppoted `GLOBAL_SCALE` constant, but assumed
inputs would always be in millimeters.
* Since input fields now show units (that are incorrect here)
the input field units needed to be converted to Blender units first.
* Then converted back to millimeters when constructing the mesh.
* Then let the addon scale the result as it expected.
