3. A silver key, even though it is made to be functional, since it is also
considered a piece of jewelry, it is permissible to carry it out [into the
public domain on Shabbos]. In contrast, it is forbidden to go out wearing
eyeglasses even when they are covered with silver (1).
(1) Nowadays, it is customary for people who need glasses in order to see
properly, to wear them in the public domain on Shabbos.