Dating antique secretary desk
A spring holds the bolt notch fast to the face of the lock housing.
The key must not only be the right size to move the bolt forward and back, it must be the right size to compress the spring and release the bolt so it can move.
This lock relies on a series of spring-loaded levers, each of different thickness to deny entry.
The most common is an inside ring of raised metal, concentric to the pin, that requires a notch in the key.
This feature is easy to overcome by inserting a new blank key in the lock and working it back and forth.
Most bolts have two notches, one in the locked position and one in the unlocked position.
In addition to correct barrel size and blade size, a lock may employ other features to prevent the entry or use of a bogus key.
This will put a mark on the blank where the notch should be and it can be cut out with a hacksaw.