Older barrel keys were used in locks on furniture, jewelry boxes and cabinets, and modern barrel keys are used in locks on vending machines, utility meters, computers, bicycle locks and ATM machines. Barrel keys have evolved from the most basic form of key to among the most difficult to copy.
Old barrel keys consisted of a barrel or tube with a bit that turned the tumbler to a lock at the end. Modern barrel locks have seven or eight pins arranged in a circular pattern that require equal tension to tumble. If the lock is turned more than one-seventh of the dial for a seven-pin lock, or one-eighth of the dial for an eight-pin lock, the pin falls back into place, making the lock extremely difficult to pick.
This lock requires the proper spacing and depth of the bits, and the correct diameter of barrel must be used. The key must be able to simultaneously press all pins at once while exerting enough force to turn the mechanism to the open position.