It is a specific type of charm that goes to a specific bracelet. I copied a description from wikipedia.
A starter Italian charm bracelet consists of eighteen blank links. In order to create a personalized Italian charm bracelet, these blank links are replaced with individually designed Italian charms. Italian charms are flat, modular links that hook together. While traditional charms dangle, Italian charms feature individual pieces soldered flat onto the surface of the link. Italian Charms are compatible across brands due to standardized sizing. The modular design means that the charms on an Italian charm bracelet are interchangeable. An individual Italian charm can be switched out for a new look or to better suit the mood or changing interests of an individual.
One of my charms is stamped stainless steel, so I think that is what they are, but I can't guarantee that. They have not rusted or turned my arm colors. Sorry I don't have more information.