The Pin Tumbler Lock

Pin tumbler locks are by far the most popular lock today. Over half of the locks in use are of the pin tumbler type. They look similar to
the wafer tumbler lock, but can easy be distinguished by their round pins, visible in the keyhole. There operation is also similar to the
wafer type, but is more costly and requires much stricter machining tolerances. Here are some diagrams: 


         |
         |
         |
         |________________________________________
         |   | @ |   | @ |   | @ |   | @ |   | @ |
         |   | @ |   | @ |   | @ |   | @ |   | @ |  Tumbler springs
         |   | @ |   | @ |   | @ |   | @ |   | @ |
         |   | @ | 4 | @ |   | @ |   | @ |   | @ |
         |   | @ |   ||~||   | @ |   ||~||   ||~||
         |___||~||___|| ||___||~||___|| ||___|| ||__ _ _ _ _ _ _Shearline
         \_  ||1|| 3 || ||   || ||   || ||   || |  |
           \_|| ||___||~||___|| ||___||~||___||~|  |
              |~|     | |     |~|     | |     | |  |
    keyway    |2|     | |     | |     | |     | |  |     Plug
              |_|     |_|     |_|     |_|     |_|  |
         +-----------------------------------------+
         |
         |
         |
         |
               The pin tumbler lock, cutaway side view (locked)
1) top pin
2) bottom pin
3) cylinder (top of plug)
4) shell



         |
         |
         |
         |________________________________________
         |   | @ |   | @ |   | @ |   | @ |   | @ |
         |   | @ |   | @ |   | @ |   | @ |   | @ |  Tumbler springs
         |   | @ |   | @ |   | @ |   | @ |   | @ |
         |   || || 4 || ||   || ||   || ||   || ||
         |   ||1||   || ||   || ||   || ||   || ||
         |___|| ||_ _|| ||___|| ||___|| ||___|| ||__ _ _ _ _ _ _Shearline
         \_  ||~|| 3 ||~||   ||~||   ||~||   ||~|  |
           \_||2||___|| ||___|| ||___|| ||___|| |  |
                      | |     |_|     | |     | |  |
    keyway            |_|             |_|     |_|  |     Plug
                                                   |
         +-----------------------------------------+
         |
         |
         |
         |
              The pin tumbler lock, cutaway side view (unlocked)

1) top pin (drivers)
2) bottom pin (key pins)
3) cylinder (top of plug)
4) shell



         ___________________                      ___________________
       _/         @         \_                  _/         @         \_
      /           @ 3         \                /           @  3        \
      |           @           |                |          | |          |
      |          | |          |                |          |2|          |
      |      ____|2|____      |                |      ____|_|____      |
      |     /    |_|    \     |                |     /    | |    \     |
      |    |    _| |_ 4  |    |                |    |    _|1|_ 4  |    |
      |    |   / |1| \   |    |                |    |   / |_| \   |    |
      |    |   | |_| |   |    |                |    |   |     |   |    |
      |    |   |     |   |    |                |    |   |     |   |    |
      |    |   |  5  |   |    |                |    |   |  5  |   |    |
      |    |   \_____/   |    |                |    |   \_____/   |    |
      |    | 6           |    |                |    | 6           |    |
      |     \___________/     |                |     \___________/     |
      |   7                   |                |   7                   |
      \_                     _/                \_                     _/
        \___________________/                    \___________________/

                Locked                                  Unlocked

        Pin Tumbler Lock (front)                Pin Tumbler Lock (front)

                                1)  bottom pin (key pins)
                                2)  top pin (drivers)
                                3)  tumbler spring
                                4)  shear line
                                5)  keyway
                                6)  plug (cylinder)
                                7)  shell

OK, I will explain how the pin tumbler lock works, but you really should consider going to K-Mart and buying a cheap lock to take apart
and study. In the lock's shell (main body) there is the keyway and three to eight (usually five) spacings drilled from the top of the lock
into the keyway. This is similar in principle to the wafer lock. In each of theses spacings are two pins and a spring. The top pins are
always the same length, while each bottom pins can each be any of ten different sizes (0-9). Note that the bottom pins have a rounded
bottom, allowing for them to ride up the key easier. The spring forces the pin stack down so that the lower pin protrudes into the
keyway. (The wedge slot keeps them from falling all the way to the bottom of the keyway) When the correct key is inserted, each pin
stack is lifted according to how deep or shallow the key is cut in that corresponding location. To open the lock, the top of bottom pin
(the point where the top and bottom pin meet) must line up with the lock plug and the shell (the shearline). When in this position, the
lock is unlocked and the plug can rotate around, taking the bottom pin around with it. If any pin is raised too high, or not high enough,
then that pin keeps the plug from turning inside the lock shell. Of course in the locked position, all the pins stop the plug from turning.

These locks are used almost everywhere. The provide over a million possible combinations for a five pin lock, and billions for the eight
pin. These are the standard door locks in most residential and commercial buildings. Often you will find pin tumbler locks with only
three pins on cheap desks, some copy machines, and storage lockers. They offer a reasonable degree of security, but are far from tamper
proof. 

Picking

Picking the pin tumbler lock is based on the principle that slight imperfections exist in every lock. Every lock is machined to certain sets
of tolerances, such as plus or minus .0002 inches. The closer the tolerance, the harder the lock is to pick, but the more expensive the
machining costs. That is what makes one pin tumbler lock harder to pick than another. This variation in the lock's components means
that in attempting to turn the plug in the lock without the proper key, one tumbler will be caught up and become tight before
subsequent tumblers are. Therefore, when turning tension is applied to the plug with a tension wrench, and the tight tumbler is lifted
with a pick, there will be either a clicking feel or a sudden relief in the tension the tumbler exerts on the pick. This relief of tension
occurs when the pin is brought up even with the shear line. At this time, lifting can be stopped.

Use a hook pick to lift each pin to its breaking point, starting with the pin that is bound (resisting) the tightest. Gently pry the pin up
against the spring pressure until it breaks at the shear line. Care must be taken not to lift the pin too high, or it may become jammed in
the upper chamber. It is often impossible to get this pin back down without releasing tension on the plug.

A common problem is applying too much tension. A light touch should be used because too much pressure on the wrench not only
makes it hard to feel any change in torsional pressure, but tends to bind all the pins, making picking order difficult to determine. The
tension wrench needs only to provide a little torque so that the pins stay up once picked. 

Raking and Vibration picking

You can also use the raking and vibration picking methods described in the section on wafer tumbler locks to pick pin tumblers. You
can even use a combination of raking and pin picking. Simply rake the pins a few times, and then go back and pick any pins that the
rake missed. You can use the hook pick to probe each pin. If the pin feels "springy" then it has not yet broke at the shear line.

Another technique: Start picking at the back pin, the one furthest away from you as you face the keyway. The reason for this is relatively
simple. The rear pin will be the last worn, and when you break it, the lock's plug will move the most it ever will for just one pin
breaking. This will make it easier to pick the other pins, as the break between the inner and outer cylinders will be progressively held
tight against the pin you are working, as you work the lock from rear to front. The reason the rear pin is least worn is that inserting a
key "rakes" the pins up and down, wearing down their sides. The rear pin is raked only once per time the key is inserted, the pin in
front of it is raked twice, and so on. Its not uncommon to see locks in which the front pin can not be picked before the rear ones. The
reason was that it was worn down to the point that no amount of torsion would cause the inner plug to put any force against it.
Consequently, it won't break. 

Rapping

Sometimes you can use a form of vibration picking known as rapping to open a pin tumbler lock. A tension wrench is inserted into the
keyway, and light to moderate tension is applied. At the same time, the face of the plug is struck sharply with a plastic mallet or
hammer handle. The rapping forces the springs and pins to gravitate toward the force of the blows. Hopefully this vibrates the picks
into their breaking positions. DO NOT HIT TOO HARD! Approach this method with caution. 

Practicing

To learn how to pick pin tumbler locks, it is best to go to the store and buy a "practice" lock. Try to find either a KwikSet brand or a
cheap Ilco lock cylinder. On top of the lock shell is a little sliding strip that covers the pin spacings. Carefully slide it out. you can then
take out the spring, the top pin, and the bottom pin. Remove all but one the assemblies and replace the cover. Now you can practice on
picking the lock with only one pin. When you become good at that, insert another stack of pins, and so on until you can pick the lock
with all five pins in place. 

Spool Pins

It is possible that in the course of picking a high security pin tumbler locks, the plug will turn a bit as if it were going to unlock, then
stop. I will turn no more than 2 or 3 degrees around. This means you have encountered a spool pin. These are simply drivers, or key
pins, or both that have had their center portions cut down to a smaller diameter. 

             ______
             |_  _|
            | |  | |  Lock body    Note that any torsion applied to the
         ___| |  | |____           cylinder will tend to catch the spooled
            ||____||               pins at their waists instead of at the
            | ____ |  Cylinder     break between the pins.  This will
            ||_  _||               either prevent the pick from pushing
            | |  | |               the pin up if the top spool is caught,
            | |  | |               or it will prevent the pin from falling
         ___||    ||____           down, if the bottom spool is caught.
             |    |
              \__/    Keyway

           spool pins


With a hook pick, you'll be able to press up on each pin and feel the difference. When you have a spool pin caught across the shear line,
gentle upward pressure will result in force in the opposite direction of the way you're turning. Determine which pins are spool pins
and push up until the bottom of the pin (assuming it's a top pin) crosses the shear line. You might lose some previously picked pins,
but just pick them again. 

Interlocking Pins

Several manufacturers have designed high security locks involving angled and interlocking pins. Emhart makes a cylinder using
angled cuts on the keys where the top and bottom pins actually interlock: 


                        +--------------+
                        |              |
                        |    Top       |
                        |    Pin       |
                        |              |
                        |              |      Interlocking Pins
                        +-----+  +-----+
                        +---+ |  | +---+
                        |   | |  | |   |
                        | +-+ |  | +-+ |
                        | | +-+  +-+ | |
                        | | |      | | |
                        | | +------+ | |
                        | +----------+ |
                        |              |
                        |   Bottom     |
                        |     Pin      |