Inside the cylinder: pins, springs, and the shear line
A standard pin tumbler cylinder contains five or six pin stacks. Each stack has a key pin at the bottom (variable height, determined by the key cut), a driver pin above it (uniform height), and a spring pushing the stack down. When the correct key is inserted, the key pins lift each stack to exactly the right height so that the gap between the key pin and driver pin aligns with the shear line — the boundary between the rotating plug and the fixed cylinder housing. When every stack aligns simultaneously, the plug rotates and the bolt moves.
Any key that fails to align even one pin stack at the shear line prevents rotation. This is why a key that is cut to the wrong pattern — including a worn copy that no longer matches the original depths precisely — fails to operate a lock consistently. The tolerances are tight.
What rekeying changes inside the cylinder
Rekeying replaces the key pins with a new set of different heights that correspond to a new key cut. The driver pins, springs, and cylinder housing stay in place. The locksmith removes the cylinder plug using a follower tool, pushes out the old key pins using the existing key or a plug-following tool, and installs new key pins matched to the desired new key. When the plug is reinserted and the new key is tested, the shear line aligns with the new cut pattern — and the old cut pattern no longer aligns it.
The operation does not alter the mechanical quality of the lock in any way. A Grade 1 deadbolt that has been rekeyed is still a Grade 1 deadbolt with exactly the same bolt strength and cycle resistance as before. The only thing that changes is which cut pattern operates the cylinder.
The rekeying process on-site, step by step
- Remove the cylinder from the door — this requires removing the interior thumbturn or the interior escutcheon plate and sliding the plug assembly out of the housing with the existing key.
- Insert the follower tool to maintain spring and driver pin position as the key pins are changed — without a follower, all the pins drop loose inside the housing and must be repacked, which takes significantly longer.
- Use the pin kit to load the new key pins matched to the cut depths of the desired new key — each pin height corresponds to a specific key cut depth, and the correct sequence must match the new blank precisely.
- Reassemble the plug with the new key pins and verify alignment — insert the new key and confirm the plug rotates freely; insert the old key and confirm it does not operate the lock.
- Reinstall the cylinder in the door and cycle the bolt multiple times with the new key to confirm operation — check that the deadbolt extends and retracts smoothly and the key extracts cleanly in both the locked and unlocked positions.
- Provide the new keys to the customer and confirm the quantity needed — additional key cuts from the new pattern can be made on-site or at a later visit.
When rekeying is not the right answer
Rekeying is not appropriate when the cylinder itself is worn, corroded, or damaged to the point where it operates inconsistently regardless of which key is used. A cylinder with worn driver pins, corroded pin stacks, or a plug that binds in the housing needs to be replaced, not rekeyed. Rekeying a failing cylinder installs new key pins in a mechanism that will continue to fail.
High-security locks with restricted keyways — Medeco, Abloy, Mul-T-Lock — require brand-specific rekeying tools and key blanks. A standard residential rekey kit will not work. Always confirm with the locksmith that they carry the appropriate tools for your cylinder brand before scheduling the visit.
Quality control checks before the truck leaves
After reassembly, technicians should verify plug cam timing with the door open and closed, confirm deadbolt throw clears the strike mortise without drag, and check that the key removes in only the approved positions. A quick spray of dry Teflon or graphite-free PTFE lube on the driver line (never oil that traps dust) keeps winter cycles smooth without attracting grit.
Photograph the pinning receipt if your building requires audit trails; some commercial leases demand proof of cylinder change after personnel events even when the hardware shell stayed the same.
- Shear test: old key fails, new key passes — three cycles minimum
- Strike drag test: bolt should not require shoulder pressure to seat
- Key extract: key should pull free at both locked and unlocked stops
Frequently asked questions
Do I need to be home for a rekey?
Yes — the locksmith needs access to the interior of the door to remove the cylinder properly. For property managers scheduling rekeys during tenant vacancies, coordinating access with building staff or leaving the unit unlocked for the appointment window is the standard approach.
Can every lock brand be rekeyed to the same key?
Locks can be keyed alike within the same brand family — all Kwikset locks to one key, all Schlage locks to one key. Kwikset and Schlage cannot share a key because they use different keyway profiles. Mixing brands while maintaining a single key requires replacing some cylinders with compatible ones, or using a master key system that bridges brands — which adds cost and complexity.
How do I know the locksmith pinned to my new key and not a random factory key?
Watch the pinning tray: each new bottom pin height should correspond to the depths printed on your key card or decoded from your chosen blank. Reputable techs hand you the first working key still smelling of brass shavings and have you sign off before cutting spares.