Locksmith - Cylinder
A cinder is the lock component where the key is inserted. A standard door knob has one keyhole, hence one cylinder. Deadbolts, however, are available in single or double-cylinder models. The double-cylinder model is operated from both sides with a key, while a single-cylinder model uses a key only from the outside and has a thumb-turn knob on the inside. Locksmiths will usually charge per cylinder when providing rekeying services.