Jantzen C-Coils are Toroidal cored inductors of extremely high power rating and extremely low DCR. The C-Coil is wound
around a toroidal sandwich core. It has extremely low resistance and
can shift a large amount of power without getting over heated. The core is formed like a donut with a round cross section and is wound from one long piece of laminated steel tape. The surface of the core is epoxy coated to secure against short circuit even at a very high load. If the stated maximum power is not exceeded the core will never saturate.
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.
Limited stock kept locally but available by special order in a range of 0.41mH to 38mH, In 12AWG to 17AWG