I bought a bag of 12 Amidon ferrite Beads, # FB-77-6301 so I could make some more inductors for my V boost circuits. I wound about ten turns of 24 gauge telephone wire on one, which is a toroidal sleeve .375" OD, .194" ID, and .41" long. I measured the inductance at 405 microhenrys, which is more than I expected.
I was reading the literature that comes with the beads, and it said that some mixes are conductive. I thought that ferrite was mostly glass, and was an insulator. So I measured one with my DMM and I found that the resistance was down in the hundreds of ohms, much _lower_ than I had expected. I had thought that I really didn't need to wind them with pvc insulated wire, but now I'm thinking that it's not such a bad idea after all. I have wound the toroids before and seen the insulation scraped off the enameled wire by the sharp edges of the totoid but I didn't think much about it. So it's possible that it could short out with the low resistance material of this particular toroid. That's something I never expected.