Thin pin

A thin pin is a master pin shorter than the minimum advised by the lock manufacturer — typically anything below 0.025″ on profiles with 0.025″ increments. Quality master keying practice rejects thin pins because they don’t sit reliably in the chamber: under spring pressure they can rotate, deform, or even slip out of position.

Thin pins are usually a symptom of poor TMK allocation. If the TMK and a change key cut at adjacent depths in the same position (e.g., TMK at 4, change key at 5 — only 0.025″ apart on a Lockwood 570), the master pin between them is one unit thick. That’s the minimum legal master pin, and “legal” doesn’t mean “good”.

Why thin pins fail in service

A thin pin of 0.025″ has limited surface area top and bottom. The driver pin pushes down on it; the bottom pin pushes up on it. Without enough material between the two contact surfaces, the master pin can:

• Tilt — sit at an angle, jamming the chamber.
• Deform — wear down under repeated key insertions, eventually losing its shape.
• Slip out — fall out of the chamber when the cylinder is removed for service, requiring re-pinning.

A system can pass MACS validation, pass the engineer’s design review, and still have multiple thin pins that quietly fail at the bench or in production.

How Keyzee handles thin pins

Keyzee’s hill-climber pass (phase 03 of the optimiser) explicitly rewrites change-key cuts where thin pins are detected. The cost function penalises any master pin under the profile’s thin-pin threshold, and the climber selects alternative cuts that respect MACS while bumping the master pin into a structurally safer range (typically ≥ 2 units).

Systems that ship through Keyzee with grade A or B have zero thin pins. Grade C systems may have a small number on profiles with very tight MACS where thin pins are sometimes unavoidable; in those cases the warning surfaces inline with the position and pin number.

Related

→ Master pin — the pin a thin pin is a sub-case of → MACS — the constraint that interacts with thin-pin generation → TMK — whose allocation determines whether thin pins emerge at all