From Supernatural Wiki:
Pestilence’s ring is a ring that helps the Green Horseman, Pestilence, channel and focus his powers. Sam and Dean obtained the ring after Castiel cut off Pestilence’s fingers using Ruby’s knife. Without it, Pestilence cannot exist on the physical plane. includes a small rare earth magnet you can easily install which brings all the horsemen rings together except war .contact me for a suitable magnetic ring for cosplay.