Many of us can remember Grandma's old dresser or Grandpa's roll top desk with the skeleton key sticking out of the keyhole.
It was amazing how antique furniture locks were used and the front door was always unlocked.
Skeleton keys are also known as barrel or bit keys. These keys would fit over a pin in the lock so the key stayed stable when turned.
If you have lost the key to your antique furniture reproductions are readily available. Many times these keys will work without any filing or blanks can be filed to fit more difficult furniture locks. You can find a large assortment here.
If you want to increase your chances of finding a working key, large reproduction antique skeleton key sets are available that even include blanks.