I already got schooled for saying that. Yes technically they're inductors, but on that board they're functioning as filters to keep the high frequency (generated by the ZVS) from going back into your main power supply. They're not part of the oscillator circuit. And besides I'm not following how switching from copper tubing to stainless changes affect of induction from the coil to the ZVS board. And I agree with Gina, stainless is going to be harder to work with, and not worth the extra effort since I don't think anyone has experienced any significant corrosion. Most people who recirculate are using a commercial coolant and those have corrosion inhibitors in them.