Shear line

=Shear Line=

The shear line is the physical point at which the plug meets the cylinder inside a cylinder-based lock. This point is where components must be properly aligned to allow the plug to rotate freely to lock or unlock the lock.

In pin-tumbler locks:
 * The lock opens once all top and bottom pins are separated at the shear line.
 * Lockpicking exploits tolerance errors in the lock to allow pin pairs to be individually separated at the shear line until the lock opens.
 * Comb picks attempts to move all pin stacks above the shear line to allow free rotation of the plug.
 * Key bumping attempts to momentarily separate pin pairs at the shear line to allow free rotation of the plug.

In wafer locks:
 * The lock opens once wafers do not obstruct the shear line.

Virtual Shear Lines
The use of master keying creates virtual shear lines. The number of virtual shear lines is a count of possible arrangements of components that allow the lock to be opened. In a normal pin-tumbler mechanism with no master keying, there is only one possible combination of components. As additional pins are added to chambers the number of possible shear lines increases exponentially. A higher number of virtual shear lines reduces the pick resistance of the lock cylinder.