Quoted from adamsebas:plastic protectors that were going around.
Someone did a run of these a few years back,you could chose the colour.The protector came with a separate smaller inner piece to replace the larger part of the ringmaster top plate that didn't affect the magnet pulse.
I have searched in the past for zero results.The metal protector,i think is a 3M stick on, a bit like a piston ring shape.Much prefer the plastic version.