The Yale Pin-tumbler invention Similar locks, with pins, were used in ancient Egypt some 4,000 years ago, but these locks were very large (approximately 30-60 cm in length) and made of wood. The pin tumbler lock is a lock mechanism that uses pins of varying lengths to prevent the lock from opening without the correct key. The the outer casing of the pin tumbler has a cylindrical hole in which the plug or metal pin is housed. The lock mechanism uses pins of varying lengths to prevent the lock from opening. To open the lock, the plug must rotate, this is done by using the correct key. The pin-tumbler design is based on a main barrel which is drilled so it has typically 5-6 cylinder slots that are set close together in a line. A metal pin, or "tumbler", fits closely to the walls of each of the slots. A second metal pin, or "driver," sits above the tumbler and is pushed down on the tumbler by a very small coil spring, which is permanently compressed as it sits inside the lock's enclosed case. Linus Yale Jr's pin-tumbler lock was similar to that which was created by Linus Yale Sr but used a smaller, flat key with serrated edges like the ones we still use today. When inserted into the lock, the key pushes the bottom pins into the right position, which allows the user to turn the key and unlock the lock.The cylinder pin-tumbler lock with the flat key was patented in 1861.