Won't stop eating metal items....

Answer 1

if he wont stop eating metal items then you should probably first take him to the vet and do what she says or is she has nothing to say and doesn't offer advice then you should try to keep as many metal items you can away from him.
Or the other opotion is to scold him if eats it again and keep scolding him whenever he does eat the metal.
He'll eventually learn to stop.