It is also very easy to use; all you need to do is wrap a pouch containing a special gel around the bottle and press a little metal disc to activate the gel. (babygearhub.net)
These contemporary drop earrings are composed of stacked metal discs. (solesociety.com)
These side exhaust outlets incorporate metal discs that keep the sound at legal levels - but they are removable, should the owner want something louder. (automobilemag.com)