I'm trying to make a boiler for brewing beer using a
central heating immersion element. I bought a circular
brass boss from my local plumbing supplier, but can't
grip the boss well enough to tighten. Are there any
squarish type boss nuts I could use for this job ?
(Obviously the thread part of the boss will have to be
circular to screw onto the immersion element thread,
but the outer part of this could be non-circular.)

Cheers

Darren