The pins of varying lengths are used to prevent the lock from opening without the correct key. Almost all the cylinder locks are based on these pin tumblers, and are also found in tubular pin tumbler locks. Lets see how it works

1. HOW A PIN TUMBLER LOCK WORKS?
The pin tumbler lock, also known as Yale lock
is a lock device in which pins of varying lengths
are used to prevent the lock from opening without
the correct key. Almost all the cylinder locks are
based on these pin tumblers, and are also found
in tubular pin tumbler locks.

2. Currently, the pin-tumbler is one of the most widely used lock designs in the world.
With a few changes in the position of pin-tumbler components, the designs can be
changed for dimple and axial or tubular locks.
Working of Pin Tumbler Lock Works?
The heart of a padlock or a Yale-type lock is a sturdy metal cylinder that can swivel
inside a sturdy metal housing. With the correct key, the cylinder can be turned freely
and the lock can be opened, but without the key or with a wrong key, the cylinder
refuses to turn and the lock stays shut.
The secret to open a lock is a series of thin metal pins that run down from the
housing into the cylinder locking it in place. There are two separate sets of pins - an
upper set and a lower set. Just above the pins is a set of small springs that keeps
them in place.
When the key is not inserted in the lock, the upper pins drop down from the housing
into the cylinder and locks it in place. Every key has a slightly different profile of
raised areas so it fits only the lock it's intended to and thus the wrong key doesn’t fits
in the lock at all. The jagged edge of the correct key into the lock pushes the pins
upward against the force of the springs. With every push of the key, the pins are
lifted more. The right key pushes all the upper pins just above the edge of the
cylinder so they no longer lock it to its housing. Thus, when the key is turned,
nothing stops the cylinder rotating, which opens the lock.
Although the basic functionality of all the Pin Tumbler Locks almost remains the
same, a little change in the cylinders changes their design.