By Allan B. Colombo
Copyright©1989, 1999, 2002
Let's take a closer look at the cylinder in Figure 4. As can be seen, the cylinder is made up of many moving parts. The center of our cylinder, into which the key inserts, is commonly called a plug. The plug has five or six holes drilled into it in a perpendicular fashion. Small pins glide up and down in these holes when a key is inserted.
The cylinder housing, into which the plug slides, also has five or six holes drilled in like fashion that correspond to the holes in the plug. As can be seen in Figure 5, these pins in the plug section correspond to those in the upper cylinder housing. The springs above them continuously apply pressure on both top and bottom pins. The bottom pins rest at the bottom of the groove that holds the key.
This groove is commonly called a keyway. When a key is inserted into the keyway, it pushes the bottom and top pins upward against the springs. The up and down pattern of the pins corresponds to the cuts on the key. If it is the proper key, it will align the pins so the junction between top and bottom pins line up with the exact spot, or shear line, between the plug and cylinder housing. When this alignment occurs, the plug will turn, thus unlocking the dead bolt or lockset.
It isn't that important that you understand all the mechanics behind how these locks work, but knowing the basic differences between them will help you in selecting the right lock for the job.
Mechanical Locks, Introduction