The Combination Lock

A combination lock is a type of lock in which a sequence of numbers or symbols is used to open the lock. The sequence is usually a specific permutation rather than a true combination. The sequence may be entered using a single rotating dial which interacts with several discs or cams, or by using a set of several rotating discs with inscribed numerals which directly interact with the locking mechanism.

Multiple-dial locks
One of the simplest types of combination lock, often used in low-security situations is the bicycle lock, which uses several rotating discs with notches cut into them. The lock is secured by a pin with several teeth on it which hook into the rotating discs. When the notches in the discs align with the teeth on the pin, the lock can be opened. This lock is considered to be one of the least secure types of combination lock.

Opening a multiple-dial lock without the combination depends on the slight irregularities in the machining of the parts. Unless the lock is machined precisely, when the pin is pulled outward, one of the teeth will pull more strongly than the others on its corresponding disc. This disc is then rotated until a slight click is...