Knuckle dusters and butt plugs are two products that never get old around here. So it's a true blessing that Etsy shop Zealeous decided to combine them in this fine piece: Ass Knuckles.
Giving new meaning to the term "ass whoopin'," the Ass Knuckles are a 3D printed design made from PLA in your choice of 10 different colors. Zealeous notes multiple times in the listing that Ass Knuckles are meant to be a novelty or gag gift, and only a novelty or gag gift. They are not intended for use as a sex toy, i.e., please do not ram them, push them, or even insert them very slowly whilst taking deep belly breaths up your or someone else's bunghole. Choose from one of my many other featured butt plugs if you're looking to do that.
Also, Zealeous doesn't specifically mention using the Ass Knuckles as a knuckle duster, but I think it goes without saying that you shouldn't try to use the Ass Knuckles as a combat weapon either.