Pin tumbler locks are the most common locks in the world. Generally speaking, this is the type of lock almost all homes, businesses, and other venues implement. Motor vehicles, however, do no utilize pin tumbler locks.
Pin tumbler locks have lower pins, and top pins. The top pins are in a row, from back to front, and have springs behind them, pushing them down. These top pins are all of the same length. Lower pins are in the “plug” of the lock. The plug is the part of the lock with the key hole; it is where you insert your key. If you look into a plug, you will probably see one or more of the lower pins suspended from the top of the plug. These lower pins are of different lengths, and the end that comes in contact with the key is usually tapered in some manner.
When you insert your key, the key pushes the lower pins upward. If it is the correct key, the lower pins will be pushed to the top of the plug, but the pins will not extend up into the upper pin chambers. The upper pins will be pushed up by the lower pins so that they are in the their chambers, and they will no longer extend into the lower plug. The lower pins and the upper pins will be butting up against each other, in a perfect line. In this condition, called a shear line, the plug can be turned (the lock can be locked or unlocked). An incorrect key would cause one or more of the upper or lower pins to extend into the opposing pin’s chamber; the plug cannot be turned.
When picking a lock, the objective is to get all of the upper pins up into their chambers while simultaneously allowing the lower pins to remain in their lower chambers WHILE also applying a slight amount of turning pressure to the plug. This picks the lock, creating an artificial condition where the plug can be turned.
Some locks have special top pins that make it difficult to create this artificial condition. These types of top pins are common in European locks, as well as in many North American pin tumbler locks. Moreover, these types of pins can be added to any pin tumbler lock, making them more difficult to pick.
As lock picking is not a common skill, spool pins are not a popular addition to a lock, and are arguably unnecessary in most instances. Most high security locks, however, have spool pins or some variation of these pins.
Oftentimes a lock is “set up” in such a manner as a long lower pin is next to a short one. This makes the creation of previously mentioned “artificial condition” created by successful picking somewhat difficult to achieve. If a long pin has short pins on either side of it, or two long pins have a short pin separating them, this makes picking even more difficult. If spool pins are added to such an arrangement, picking the lock becomes very difficult.
To ascertain how difficult (or easy) it is to pick your own lock, look at your key. The various cuts in the key indicate the length of the lower pins in the lock. Short cuts next to long cuts indicate that picking would be more difficult, while a series of short cuts may indicate that picking is not that difficult.
Of course, the above assessment does not take into account the skill of the person picking the lock. Good locksmiths usually enjoy the challenge of picking a lock, irrespective of the level of difficulty.
