الجواب حامدا و مصلیا
In it’s pure essence there is no effectiveness as such in any object made of metal. However if the purpose is to have protection from Black Magic etc., it is Sunnath and an act of experience to recite Muwwizathain (Sura e Al Falaq and Sura e Al Naas) and blow in hands and apply it all over the body for protection including Black Magic and various other diseases and this practice should be adopted vigilantly.
Allah knows best.