Jantzen C-Coils are Toroidal cored inductors of extremely high power rating and extremely low DCR. These coils are heavy !
In his book 'High Performance Loudspeakers', Martin Colloms praises the virtues of Toroids including low distortion and self screening of stray magnetic fields.
Note - The inductance value needs to be measured at 100Hz - The range where they are typically used as an inductor for the bass driver.
Typical handheld LCR meters measure at 1,000 Hz and will read a lower value than labelled. This is not a fault of the inductor.
They should be used in Bass crossovers only due to core distortion at higher frequencies.
Limited stock kept locally but available by special order in a range of 0.41mH to 38mH, And 12AWG to 17AWG