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How a Key opens a Lock
This
chapter presents the basic
workings of
pin tumbler locks, and the
vocabulary used in the rest of this
booklet. The terms used to describe
locks and
lock parts vary from
manufacture to
manufacture and from
city to
city, so even if you already
understand the basic workings of locks, you should
read this.
Knowing how a
lock works when it is opened by a key is only
part of what
you need to know. You also
need to know how a lock responds to
picking. Chapters
3 and
5 present
models which will help you understand a lock's
response to picking.
The
key is inserted into the
keyway of the plug. The
protrusions on the side of the
keyway are called
wards.
Wards restrict the set of
keys that can be inserted into the
plug. The plug is a
cylinder which can rotate when the proper
key is fully inserted. The non-rotating part of the
lock is called the
hull. The first
pin touched by the key is called
pin one. The remaining pins are numbered
increasingly toward the
rear of the lock.
The proper key lifts each pin pair until the gap between the
key pin and the
driver pin reaches the
sheer line. When all the pins are in this
position, the plug can rotate and the lock can be opened. An incorrect
key will leave some of the pins
protruding between the hull and the plug, and these pins will prevent the plug from
rotating.