Shear line (locksmithing)

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In a cylinder lock, the shear line (also known as the split line in Australia), is where the inner cylinder ends and the outer cylinder begins. When a break in the pin is reached by picking, the pin will "hang" at the shearline due to the space between the inner and outer cylinder. This "imperfection" in the lock mechanism is an unavoidable defect in the manufacturing process that allows for lock picking. Lock picking is a vital part of the locksmithing process as it can grant non-destructive entry to the lock device thus allowing it to be rekeyed instead of being replaced.

Lock picking the art of unlocking a lock without the original key

Lock picking is the art of unlocking a lock by manipulating the components of the lock device without the original key.

Rekeying a lock is replacing the old lock pins with new lock pins. Locks are usually re keyed to build master-key systems, make a set of locks share a common key, or to eliminate compromised keys. Sometimes worn pins are replaced with new pins if the old pins become too short to reach the shear-line. The shear-line is the thin line shared by the lock plug and its cylindrical housing. If a pin sits flush with the circumference of the plug it will allow lock rotation. Lock cylinders use different length pins in different combinations to create relatively unique key bitting. Most keys have 5 cuts from bow to tip. If a key has 5 cuts, the lock has 5 pins. Different brand locks each vary in many small ways, this is most true when servicing them. Many manufacturers offer product-specific manuals. Information disclosed in manufacturer manuals is often otherwise difficult to find, as is locksmith material in general.

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