Follower Shim: Definition, Purpose, and Service Considerations
Follower Shim is a thin service insert used when working on a lock cylinder so the plug can be removed or repositioned while the pin stacks remain controlled. In practice, a Follower Shim helps reduce the chance that top pins and springs migrate into the plug chambers during service.
Because a Follower Shim is primarily a tool for controlled disassembly, it is discussed most often in the context of repinning, core servicing, and other work where the plug is separated from the shell. The term Follower Shim is also used as a shorthand for the specific shim profile selected to match a given lock cylinder geometry.
What Is a Follower Shim
Plain Language Definition
A Follower Shim is a thin strip (often metal or polymer) that is inserted alongside the plug during service to guide or “follow” the plug as it is withdrawn. The goal of a Follower Shim is not to unlock a door or bypass security; it is to keep internal components aligned while the lock cylinder is opened for legitimate maintenance.
In many service routines, the Follower Shim acts as a controlled barrier between the plug chambers and the shell chambers. When the plug is pulled, the Follower Shim maintains a continuous surface so driver pins and springs do not drop into the plug area.
Where It Is Used
A Follower Shim is commonly associated with pin tumbler lock cylinder service, including rekeying and repinning tasks where the plug must be extracted. A Follower Shim may also be used on certain interchangeable core formats when the service method calls for controlling the top stacks during plug movement.
In training materials, the Follower Shim is typically presented as a companion to a plug follower and a shim set, but the phrase Follower Shim should be understood as the specific thin insert that matches the lock cylinder’s clearance requirements. In some workholding setups, a Follower Shim is used to reduce friction and protect the plug face as it slides out.
Follower Shim security profile and design
Follower Shim design is driven by clearance, stiffness, and the need to avoid damaging internal surfaces. A shim that is too thick can bind the plug, scrape the shell, or deform spring pockets; a shim that is too thin may buckle and allow parts to shift.
From a security standpoint, a shim is a servicing aid rather than a security defeat method. The shim is used after a lock cylinder is already in a controlled service state, typically with the plug positioned so the work can proceed without uncontrolled pin movement. The shim’s function is to preserve internal order, not to change the lock’s keying on its own.
Follower Shim handling also matters. A shim that is inserted at an angle can catch on pin chambers, and a shim that is forced can score soft metals. For that reason, shim selection is often matched to the specific lock cylinder family, and the shim is inserted with consistent alignment to the plug.
Some technicians treat the shim as disposable when it becomes bent or burred. A worn shim can introduce drag, create false feedback, or shed small fragments that contaminate the lock cylinder. In controlled shop practice, the shim is inspected before use and replaced when its edge profile is no longer uniform.
Security and Service Considerations
Frequent service problems
A shim is often discussed when a service attempt results in a pin-stack spill. If the plug is pulled without a correctly fitted shim, driver pins and springs can migrate into the plug chambers and jam the assembly. Once that happens, the lock cylinder may require full teardown, cleaning, and repinning.
Another frequent issue is mismatched thickness. A shim that does not match the clearance of the plug and shell interface can deform, wedge, or twist. When a shim twists, it may allow partial movement of the top stacks and create a mixed stack condition that is time-consuming to sort.
Edge damage is also common. A shim with sharp burrs can scratch the plug or shell. If a lock cylinder is already worn, an aggressive shim edge can worsen drag and contribute to rough key feel after reassembly.
Work that uses the Follower Shim
Several legitimate maintenance tasks use a shim as a control step. A shim is used during plug removal for repinning, during core maintenance when internal contamination is present, and during corrective work when a prior service attempt displaced internal parts.
A shim can also be used during diagnostic teardown to confirm whether a binding condition is due to internal misalignment versus external keying issues. In that workflow, the shim helps ensure that disassembly does not create additional faults that obscure the original problem.
When a lock cylinder is part of a restricted key system or a property key-control program, the shim is treated as a routine bench tool rather than a special-purpose device. The shim is simply part of the process of opening the lock cylinder while keeping the top stacks managed.
Technical specifications
| Reference item | Notes |
|---|---|
| Follower Shim | Thin insert used during lock cylinder plug movement to maintain controlled separation between plug chambers and shell chambers. |
| Material | Varies by product; material choice is typically based on stiffness, edge finish, and wear characteristics. |
| Thickness profile | Selected to match the clearance of the lock cylinder being serviced; incorrect thickness can cause binding or buckling. |
| Edge condition | Edges should be uniform and free of burrs to reduce scoring of the plug and shell surfaces. |
| Use condition | Often replaced when bent, creased, or contaminated; a damaged Follower Shim can increase service risk. |
In documentation and training, the term shim is sometimes used generically. For accurate service planning, the shim should be understood as a specific profile chosen for the lock cylinder at hand rather than a one-size universal insert.
Related from Low Rate Locksmith: Follower Set, Cylinder Shim, Door Stop, Drilled Keyway.
Follower Shim support
For on-site lock hardware troubleshooting and controlled lock cylinder service, contact Low Rate Locksmith at (833) 439-8636. A service dispatcher can help route the request and confirm the tool-and-parts approach appropriate for the lock cylinder involved, including when a shim is indicated.