A wafer (or wafer tumbler, disc tumbler, plate tumbler) is a type of lock design that uses flat metal locking components to directly block rotation of the plug. Wafer keys position all wafers at the shear line to allow the plug to rotate freely.
Wafer locks are popular in a variety of environments, and are classified as low to medium security. Low-security cabinet, desk, and drawer locks are commonly a wafer design. Wafer locks are also the most common form of automobile lock, with many newer models integrating electronic components.
Disc-detainer lock designs use similar locking components, but are instead characterized by round disks that are rotated by the key.
The earliest wafer designs were developed by P. S. Felter in 1868 and Hiram S. Shepardson in 1870. In the 1930s Chicago Lock and Briggs Stratton began producing wafer locks that used a sidebar.
Principles of Operation
A set of wafers is used to block rotation of the plug at one or more points. Low-security wafer locks traditionally block at a single point, though more advanced models can block at the top and the bottom, as well as alternate the bitting of components to be at the top and bottom of the keyway. When the correct key is inserted, all wafers are properly positioned and the plug is free to rotate and engage the bolt mechanism.
Master keying is made possible by wafers with stepped or otherwise segregated bitting areas that interact with the change and master keys.
- A flat piece of metal placed in the plug of the lock as the primary locking mechanism. Each wafer may have a different size or a different protrusion in the center to provide differs. When wafers are positioned so that they are not protruding from the plug, the plug and cam can rotate to lock or unlock the lock.
- On the side(s) of wafers a spring is used to bias wafers out towards the cylinder.
- The plug is the inner piece of the lock that rotates upon insertion and tension of the correct key. The plug is connected to the cam to actuate the bolt mechanism when rotated.
- The cylinder is the outer piece of the lock that houses the plug. The cylinder is responsible for blocking rotation of the plug when wafers protrude from the plug.
- The cam is an extension connected to the back of the plug which actuates the bolt mechanism to lock or unlock the lock.
Wafer locks are vulnerable to a variety of attacks:
- Wafer locks are not vulnerable to key bumping or pick gun attacks because they do not use pin-tumblers. Bumping a wafer lock will damage the wafers and may cause the bump key to get stuck in the lock.
- Low-security wafer locks are also subject to visual decoding based on the resting position of each component.