Disc tumbler lock

A disc tumbler lock or wafer lock is a type of lock that utilizes a set of flat discs to prevent the lock from opening unless the correct key is inserted.

Without a key in the lock, the discs (red) are pushed down by springs. The discs nestle into a groove in the lower part of the outer cylinder (green) preventing the plug (yellow) from rotating.

When the correct key is inserted, the discs (red) are raised up out of the lower groove in the outer cylinder, but not so high that they enter the upper groove in that cylinder.

With the discs unobstructed, the key, discs, and plug (yellow) can rotate.

Design

In a cylindrical disc tumbler lock, a series of flat discs or wafers holds a cylindrical plug in place. The discs are fitted into vertical slots in the plug, and are spring-loaded, causing them to nestle into a wide groove in the outer casing of the lock. This groove blocks the discs from rotating, which in turn prevents the plug from rotating.

A rectangular hole is cut into the center of each disc; the height of the holes in the discs vary in size, so a key must have notches corresponding to the height of the hole in each disc in order to open the lock.

When the correct key is inserted, the discs are raised to a height sufficient to allow them to clear the groove in the outer casing. The discs must not be raised too high, or they will enter a second groove on the opposite side of the casing, preventing the discs from rotating. When all the discs are clear of both grooves, the plug, along with the discs and key, may rotate.