marco,
on top of one of my early coils (3"-20")i used one of those compression
type pvc connectors for sink installations i believe. i then mounted my
toroid onto a 12" length of 1 1/2 pvc, stuck it into the compression
fitting, then i could loosen the locking ring and raise or lower it then
tighten it to try.
i still have that coil , if you would like i'll send you a picture of
the set up.
marc