It is a ball for a a construction keyed lock, and when the home builder is done and the new home owner inserts their key, the cuts on their key are a little different than the contractors key and when the lock is turned
the first time, it drops a ball off into the side holes and it changes the key combination of that lock and makes it so only the new home owner's key works, and the home builder's key no longer works.
read more here:
https://www.lockpicking101.com/viewtopi ... =3&t=61506
