Shear line

Shear Line

A plug with the pin-tumblers properly aligned at the 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 and 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.

See also

• Plug
• Cylinder
• Lock
• Key
• Master Keying

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