Most key rings are made of steel. If you intend to use a magnet to find or retrieve the key.
Itīs not quite true that stainless steel is non magnetic. It depends mostly on the portions of nickel and cobalt. There is austenitic steel which is non magnetic and ferritic steel which is magnetic. Only ferritic steel can be hardened because hardening depends on a change in crystal structure of steel during quenching. Austenitic steel does not have this change in crystal structure. That is why cutting tools and cutlery usually are magnetic.
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If it isnīt broken, it doesnīt have enough features yet.