Rogowski Coil
Form for a Rogowski coil. Useful for measuring the net current passing through the loop. This particular coil form was used to acquire data that was ultimately published in RSI, thereby proving the value of my home 3D printing hobby. (That is, it has some nonzero value. Costs are a totally different thing.) To learn more about what this thing is used for, see http://en.m.wikipedia.org/wiki/Rogowski_coil.