Four-wheel combination locks use a single dial which must be rotated left and right in a certain combination in order to open the lock. Rotary combination locks are used on a verity of safes & Vaults. These offer extra protection of an additional number to be dialled in than the 3 wheel.
Within the locks are Four mechanism discs, with notches that must be aligned to allow the lock to open. When entering the set code, you would start by turning the wheel to the set numbers set in the lock – The process is completed back and forth until all discs are in place, and the lock is released.