model that highlights
interactions between pin positions. Chapter 4 uses this model to explain how picking
works. Chapter 9 will use this model to explain complicated mechanical defects.In order to become
good at picking locks, you will need a detailed understanding of how locks works
and what happens as it is picked. This document uses two models to help you understand
the behavior of locks. This chapter presents a model that highlights
interactions between pin positions. Chapter 4 uses this model to explain how picking
works. Chapter 9 will use this model to explain complicated mechanical defects.
The
"flatland" model of a lock is shown in Figure 3.1 This is not a cross
section of a real lock. It is a cross secrtion of a very simple kind of lock.
The purpose of this lock is to keep two plates of metal from sliding over each
other unless the proper key is present. The lock is constructed by playing the
two plates over each other and drilling holes which pass 
through both plates. The figure shows a two
hole lock. Two pins are placed in each hole such that the hap between the pins
does not line up with the gap between the plates. The bottom pin is called the
key pin because it touches the key. The top pin is called the driver
pin. Often the driver and the key pins are just called the driver and the
pin. A protrusion on the underside of the bottom plate keeps the pins from falling
out, and a pring above the top plates pushed down on the driver pin.
If
the key is absent, the plates cannot slide over each other because the driver
pins pass through both plates. See Figure 3.3. That is, the key lifts the key
pin until its top reaches the lock's sheer line. In this configuration the plates
can slide past each other. 
Figure 3.3 also illustrates one of the important features of real locks. There is always a sliding allowance. That is, any parts which will slide past each other must be separated by a gap. The gap between the top and bottom plates allows a range of keys to open the lock. Notice that the right key pin in Figure 3.3 is not raised as high as the left pin, yet the lock will still open.
{page8 - diagrams p8a, p8b, p8c: labeled a] Figure 3.1: Flatland model of a lock b] Figure 3.2: (a) Flatland key raised pins c] Figure 3.3: (b) Proper key allows plates to slide. }