Just a normal chinch plug you would use for cables.... the plus pin is extended with 2,5mm2 OFC copper to the end of the plug, then the chinch plug gets screwed together, you fill it up with some crystal powder/granulate, you put some isolation tape on the end, then finish it up with conducting copper foil, closing the plug "electrically", so the extended plus pin doesnt act as a antenna, the isolation tape just makes sure you dont short the copperfoil (ground) to the plus pin
tho i would be still careful, you could push the end in and still short through the isolation tape, if you wanna play save you make the plus extender 5-10mm shorter than the plug
also you need to watch out for what plugs you use... not all are conducting till the end... you need one solid metal one where the shell is connected to ground for most effectiveness, the ones i used are these:
https://www.hotsound-store.com/dynavox-cinchstecker-carbon-4er-set-vergoldet-7220
my latest ones were tourmaline with roughly 20% quartz, pretty happy with them, also the finer tourmaline powder i got is more effective than the DIY granulate i made before