Hello PFs, I need to build some Helmholtz coils, and I was wondering if anybody here had suggestions on what to make the actual rims that hold the wire in a coil are generally made out of? So far its been suggested that I use bicycle rims, but even that creates a question--aluminum or steel? Should the rims be ferromagnetic or paramagnetic? Anybody have experience building these? I was hoping to make mine about a bit less than a meter in diameter.