My sons wanted hypnorings like in the Captain Underpants books. They made color illustrations and everything, so I obliged.This design requires a dual extruder printer.Warning, do not use this on your elementary school principle to convince them they are a super hero. Seller will not be held responsible for any incredulous adventures that may occur from the use of your glow-in-the-dark hypnoring. For use with https://www.youmagine.com/designs/stubby-sized-ring-a-thingI printed up a couple extras that I put up for sale on Etsy.http://etsy.com/listing/109577605/glow-in-the-dark-hypnoring