The basics of the pin tumbler lock goes back to 2000 BC in Egypt. the lock consisted of a wooden post affixed to the door, and a horizontal bolt that slid into the post. The bolt had north to south openings into which fitted a set of pins. These could be lifted, using a key, to a sufficient height to allow the bolt to move and unlock the door.



Inventor Linus Yale, Sr. patented a pin tumbler lock in 1848, a designthat was improved and patented by his son, Linus Yale, Jr. He did this in 1861 Yale, Jr.'s is the same design used in pin tumbler locks today.

The pin tumbler is most commonly used in cylinder locks but is used in other applications also. In this type of lock, an outer casing has a cylindrical hole in which the plug is housed. To open the lock, the plug must rotate.

The plug has a straight shaped slot known as the keyway at one end to allow the key to enter the plug; the other end may have a cam or lever which activates a mechanism to retract a locking bolt. The keyway often has protruding ledges which serve to prevent the key pins from falling into the plug, and to make the lock more resistant to picking. A series of holes, typically five or six of them, are drilled vertically into the plug.

These holes contain key pins of various lengths, which are rounded to permit the key to slide over them easily.

Above each key pin is a corresponding set of driver pins, which are spring-loaded. Simpler locks have only one driver pin for each key pin, but locks requiring multi keyed entry, such as a group of locks having a master key, may have extra driver pins known as spacer pins. The outer casing has several vertical shafts, which hold the spring loaded pins.

Locksmithing this type of lock is a basic part of locksmith training and is one of the most common types of locks worked on by locksmiths on a daily basis.

When the plug and outer casing are assembled, the pins are pushed down into the plug by the springs. The point where the plug and cylinder meet is called the shear point. With a key properly cut and inserted into the groove on the end of the plug, the pins will rise causing them to align exactly at the shear point. This allows the plug to rotate, thus opening the lock. When the key is not in the lock, the pins straddle the shear point, preventing the plug from rotating.

Sets of locks with a master key will have one set of shear points that are identical to the others in the set and one set that is unique to that specific lock.

This is one of the simple locks and one that provides adequate security for the average consumer