How Is A Key Able To Operate My Lock?

Mortise Lock Cylinder

A key has a head and a shank. The shank of the key contains information that is important to the lockset that you have. The millings down the sides of the key must be correct or the key will not fit into the lock cylinder plug. If you take your key and look down the shank from the tip of the key, you will notice that there are millings on both the sides of your key that form a specific pattern. The exact opposite and accommodating pattern can be found on the plug inside of your lock. This is known in locksmith terms as the keyway but more commonly referred to as the key hole. If you look at the profile of the key shank you will notice that there are bumps and flat portions in the cuts of the key. The flat portion is where each individual bottom pin rests when the key is fully inserted into the lock.

The lock bottom pins (see diagram), that is, those that sit on the flat part where the key has been cut are available in varying lengths and measured in thousandths of an inch. These bottom pins are available in increments of three or five thousands of an inch starting at .160 thousands right up to and including .360 thousands of an inch. This provides a certain measure of accuracy when a professional locksmith is repining a lock cylinder.

The plug (see diagram) is the round portion that contains the keyway or key hole. It is the part of the lock that is able to turn when the correct key is inserted into the lock. When the plug turns it is able to actuate the locking mechanism allowing someone to engage or disengage the bolt or spring latch from the door frame. In order for the plug to be able to turn, the correct key must be inserted into the plug. The pins must all be the right length to correspond with the cuts in the key or the plug cannot turn. If even one bottom pin is the incorrect length the plug will not be able to turn. When the correct key is inserted into the keyway and all the bottom pins are raised to their correct level, the plug is allowed to turn and the key will operate the lock. When this happens, professional locksmiths refer to this as the lock cylinder shear line (see diagram).

We want to provide you with a complete picture of the lock cylinder. You should be aware that although there are bottom pins inside of a lock, there are also top pins (see diagram). There is also a spring in each chamber of a lock. Each chamber that houses each spring, top pin and bottom pin is spaced out in the lock cylinder. This means that the spacings of the cuts in the key need to be fairly accurate. For your information, in a pin tumbler type lock cylinder there could be 5, 6 or even 7 chambers that can accept the spring/pin combination. The more chambers in use in a lock cylinder, the higher the degree of skill required to be able to pick the lock open.

The drawn diagram, displayed for educational purposes, is a correct and fairly accurate depiction of the cross-section of a lock cylinder. We have attempted to illustrate the definitions we have provided in this blog post through this hand-drawn diagram.

We hope that this article has provided you with some insight as to how a lock cylinder is put together and operates.

Security Article Written by: Toronto Locksmith


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