Master Keying
Core concepts
Master keying lets one key open many locks while change keys open only their own. Understand the master key system hierarchy: grand master, master, sub-master, and change keys. Know how a master key works through split pins: a two-level system uses pins split at the master shear line so the master key raises all pins to one shear line and the change key to another. Learn the concepts of progression, rotation, and the number of usable levels, and how pinning charts are built. Understand that master keying reduces security because more keys can operate a given lock.
Traps to watch
A frequent trap is assuming a master key system has unlimited levels; each additional level consumes pinning options and can create key interchange (a change key operating another lock). Questions may ask why master keying weakens security: more shear lines mean more possible operating keys. Another trap is confusing a master key with a grand master. Also beware of assuming all pins must be split; only those needed for the levels are split.
Rule of thumb
Every added level costs pinning room and increases interchange risk. Build the system from the top down and test for interchange before issuing keys.
Worked example
A two-level system uses pins split so the master key aligns all splits at the upper shear line and the change key at the lower. If a third level is added, some pins must support three positions, and the risk of a change key opening a neighboring lock rises. The correct design step is to verify no change key operates another lock before cutting.
Professional Practices, Ethics, and Safety
Core concepts
This domain covers how a locksmith conducts business and stays safe. Know the importance of verifying authorization before opening or rekeying: proof of residency, ID, work order, or property ownership. Understand documentation practices (invoices, work orders, key control records) and the ethics of confidentiality, honesty in pricing, and refusing work that appears unlawful. Safety topics include eye protection when drilling or cutting, hand protection when handling springs and sharp key blades, proper ventilation when using solvents, and safe lifting of doors. Know basic electrical safety when servicing electronic locks and the importance of not defeating life-safety hardware.
Traps to watch
Questions often test whether a locksmith should open a door for someone who cannot prove authorization; the answer is to verify first, even if it inconveniences the customer. Another trap is life-safety hardware: never disable or block fail-safe egress hardware. Watch for questions that reward the cheapest or fastest option over the ethical one. Also beware of assuming a verbal claim of ownership is sufficient.
Rule of thumb
If you cannot verify authorization, do not open the lock. If a device is life-safety related, do not compromise its egress function.
Worked example
A person asks a locksmith to open an apartment door and says the lease is in a roommate's name. The correct response is to request proof of residency or authorization, or to decline until verification is provided. Opening without verification violates professional practice even if the request seems genuine.