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newSchoolWorks.com › VoTechWorks › Business & Cross-Cutting › Locksmith & Security Systems › Keying Systems: Master Keying, Rekeying, and Key Control › Lesson 1
BUS-LOCK72-03 · Lesson 1 · 13 clock hours · lab

Pin-Tumbler Cylinder Anatomy and Rekeying Fundamentals

Objective. The student will disassemble, rekey to a specified bitting, and reassemble a pin-tumbler cylinder so that only the new key operates the plug without binding or false set.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a credentialed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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How a Pin-Tumbler Cylinder Works

The pin-tumbler cylinder is the most common lock mechanism in North American residential and commercial hardware. Understanding its anatomy is the foundation of every rekeying job you will perform.

A pin-tumbler cylinder has two main metal bodies: the shell (also called the outer cylinder or housing) and the plug (the rotating inner cylinder that the key enters). The plug sits inside the shell and is held in place rotationally by the pin stacks.

The Pin Stack

Each pin stack occupies one vertical chamber that passes through both the shell and the plug. A standard residential cylinder has five pin stacks; many commercial cylinders have six. Each stack contains:

When no key is inserted, driver pins cross the shear line — the interface between the top of the plug and the inside of the shell — and lock the plug in place.

When the correct key is inserted, each key cut lifts its bottom pin by a precise amount. If every bottom pin is lifted exactly to the shear line simultaneously, every driver pin is pushed entirely into the shell chamber. The shear line is clear all the way around, and the plug rotates freely to operate the lock.

If any one bottom pin is too short (undercut) or too tall (overcut), part of a pin stack will still cross the shear line and the plug will bind or stop.

Bitting and Bitting Specifications

Bitting refers to the pattern of cut depths on a key blade. Each cut is assigned a number — the bitting number — from a manufacturer's specification chart. Kwikset uses a depth increments system with cuts numbered 1 through 6 (deeper numbers indicate deeper cuts). Schlage uses its own depth series. Always reference the manufacturer's bitting specification sheet for the correct pin size that corresponds to each bitting number. Using the wrong sheet for the wrong brand will produce a non-functioning cylinder.

A written bitting specification for a job might read: 3-1-4-2-5 (five positions, reading bow to tip). Each number tells you which bottom pin to place in that chamber.

Rekeying: The Process

Rekeying means replacing the bottom pins so that a different key operates the cylinder. The shell, driver pins, springs, and plug remain in place; only the bottom pins change.

Tools you will use:

Step-by-step overview:

1. Insert the existing key and turn the plug to the service position (typically 90°) if the design requires it, or keep it at 0° per manufacturer instructions.

2. Push the plug follower in from the rear of the cylinder, following the plug out the front. The follower now holds all driver pins and springs in the shell.

3. Hold the plug over the pinning tray, remove the existing key, and use tweezers to remove each bottom pin into its labeled tray position.

4. Read the new bitting specification. Select the correct bottom pin for position 1 from the pinning kit, place it in the plug chamber for position 1. Repeat for all positions.

5. Insert the new key. Each bottom pin should sit flush at or just below the top of the plug chamber; none should protrude above it.

6. Align the plug keyway with the shell, then push the plug straight back into the shell while simultaneously withdrawing the follower from the rear. This loads each driver pin and spring back onto its bottom pin.

7. Test: the new key should turn smoothly without binding. Two test keys with adjacent bittings should not open the lock.

False Set and Binding

A false set occurs when the plug rotates a few degrees and then stops. This usually means one pin stack is positioned so that the driver pin is resting on the edge of the plug rather than fully in either the plug or the shell. Common causes: a bottom pin selected one size too tall or too short, or a driver pin that was not reseated properly during assembly.

Binding with the correct key usually means a pin is the wrong size for the bitting or the plug was misaligned on re-insertion.

Safety and Bench Practices

Key terms10

PlugThe rotating inner cylinder of a pin-tumbler lock that the key enters; it turns to operate the locking mechanism when the shear line is clear.
ShellThe fixed outer housing of a pin-tumbler cylinder that surrounds and contains the plug, springs, and driver pins.
Shear lineThe precise interface between the outer diameter of the plug and the inner diameter of the shell; the lock opens only when all pin stacks are flush at this line.
Bottom pin (key pin)The pin in a stack that contacts the key blade directly; its height is determined by the bitting of the key and controls whether that stack clears the shear line.
Driver pinThe upper pin in a stack, located in the shell chamber; it blocks rotation by crossing the shear line unless lifted entirely into the shell by the correct key.
BittingThe pattern of cut depths on a key blade, expressed as a numeric code where each number corresponds to a specific bottom-pin height per the manufacturer's specification chart.
Plug followerA cylindrical tool the same diameter as the plug, pushed in from the rear during disassembly to keep driver pins and springs in the shell while the plug is removed.
False setA condition in which the plug rotates a small amount and then stops, caused by a driver pin resting on the shear line edge rather than being fully in one chamber.
RekeyingThe process of replacing only the bottom pins in a cylinder so that a new key operates it and the previous key no longer works.
Pinning trayA divided tray used to hold and organize pin stacks by chamber position during disassembly and rekeying, preventing mix-ups and loss of components.

Worked examples4

1. A Kwikset bitting specification sheet shows that bitting number 1 = 0.150 in. pin height, bitting number 2 = 0.165 in., and each successive number adds 0.015 in. A cylinder must be rekeyed to the bitting 3-1-4-2-5. What bottom-pin height (in inches) is required for position 3?
  1. Identify the formula: pin height = 0.150 in. + (bitting number − 1) × 0.015 in.
  2. Position 3 has bitting number 4: pin height = 0.150 + (4 − 1) × 0.015
  3. Calculate: (4 − 1) = 3; 3 × 0.015 = 0.045
  4. Add: 0.150 + 0.045 = 0.195 in.
Answer: The bottom pin for position 3 must be 0.195 in. tall (bitting number 4 on this Kwikset depth series).
2. Using the same Kwikset depth series (bitting 1 = 0.150 in., increment = 0.015 in. per step), you measure a removed bottom pin with a micrometer and read 0.180 in. What bitting number does that pin correspond to?
  1. Rearrange the formula: bitting number = ((measured height − 0.150) / 0.015) + 1
  2. Subtract base: 0.180 − 0.150 = 0.030
  3. Divide by increment: 0.030 / 0.015 = 2
  4. Add 1: 2 + 1 = 3
Answer: The pin corresponds to bitting number 3.
3. You are rekeying all five chambers of a Kwikset cylinder to the bitting 2-4-1-3-5. Using the same depth series, list the required bottom-pin height in inches for each of the five positions.
  1. Apply pin height = 0.150 + (bitting − 1) × 0.015 for each position.
  2. Position 1, bitting 2: 0.150 + (1 × 0.015) = 0.165 in.
  3. Position 2, bitting 4: 0.150 + (3 × 0.015) = 0.150 + 0.045 = 0.195 in.
  4. Position 3, bitting 1: 0.150 + (0 × 0.015) = 0.150 in.
  5. Position 4, bitting 3: 0.150 + (2 × 0.015) = 0.150 + 0.030 = 0.180 in.
  6. Position 5, bitting 5: 0.150 + (4 × 0.015) = 0.150 + 0.060 = 0.210 in.
Answer: Position 1 = 0.165 in., Position 2 = 0.195 in., Position 3 = 0.150 in., Position 4 = 0.180 in., Position 5 = 0.210 in.
4. After rekeying, you test the cylinder with a key cut to bitting 3-1-4-2-5 and a second key cut to 3-1-4-3-5 (one bitting number higher in position 4). The second key turns the lock. Using the depth series above, by how many thousandths of an inch do the position-4 bottom pins differ between the two bittings, and what does this tell you about the rekey?
  1. Position 4 on correct key is bitting 2: pin height = 0.150 + (1 × 0.015) = 0.165 in.
  2. Position 4 on test key is bitting 3: pin height = 0.150 + (2 × 0.015) = 0.180 in.
  3. Difference: 0.180 − 0.165 = 0.015 in. (one depth increment).
  4. If the second key also opens the lock, the bottom pin installed in position 4 is 0.180 in. (bitting 3), not 0.165 in. (bitting 2). The wrong pin was installed, or the correct pin was placed in the wrong chamber.
Answer: The two pins differ by 0.015 in. The fact that the adjacent-bitting key opens the lock proves the wrong bottom pin (0.180 in. instead of 0.165 in.) is in position 4; the cylinder must be disassembled and corrected.
In class: Instructor demonstrates full disassembly of a Kwikset and a Schlage cylinder on a workbench camera, identifying each pin stack component (driver, bottom pin, spring, plug, shell) by name before students attempt the same on their own cylinders · Students use a plug follower, follower rod, and pinning tray to remove old pin stacks, select new bottom pins from a pinning kit using a pin gauge to match a written bitting specification, reassemble, and verify correct function by testing with the specified key and two incorrect keys · Pairs of students trade cylinders, attempt to decode the bitting by feel using a pick and tension wrench (with instructor guidance), then compare decoded bitting to the written spec to reinforce understanding of how pin heights control shear line
Materials: Kwikset and Schlage cylinders (minimum two per student), plug follower set, follower rods, pinning trays, pin tweezers, pinning kit with full range of bottom and driver pins, plug and shell follower rods, tension wrenches, key gauge/micrometer, Kwikset and Schlage bitting specification sheets, ALOA Technical Reference Library excerpts on pin-tumbler operation
Check: Student rekeyed cylinder operates smoothly on specified key and rejects two adjacent-bitting test keys; instructor inspects plug seating and spring tension; pass = cylinder functions correctly and student can name each pin-stack component; 100% of steps completed without damaging cylinder

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Lock Mechanisms and Key Control
1. What is the PRIMARY function of the driver pin in a pin-tumbler cylinder when no key is inserted?
Lock Mechanisms and Key Control
2. A locksmith inserts the newly cut key into a rekeyed cylinder and finds that the plug rotates about 15 degrees and then stops firmly. This symptom is BEST described as:
Lock Mechanisms and Key Control
3. When using a plug follower during cylinder disassembly, the follower is pushed in from the REAR of the cylinder. What would happen if you removed the plug WITHOUT using a follower?
Lock Mechanisms and Key Control
4. A bitting specification for position 2 of a Kwikset cylinder calls for bitting number 5. Using a depth series where bitting 1 = 0.150 in. and each step adds 0.015 in., what bottom-pin height must be selected?
Lock Mechanisms and Key Control
5. You are rekeying a Schlage cylinder but accidentally use a Kwikset bitting specification sheet to select bottom pins. What is the MOST LIKELY outcome?
Workplace Safety and Trade Practices
6. Which personal protective equipment is MOST important to wear during pin-tumbler rekeying at the workbench?
Lock Mechanisms and Key Control
7. After rekeying, a student tests the cylinder with the specified new key and with an adjacent-bitting key (one bitting step different in one position). The adjacent-bitting key ALSO opens the cylinder. What is the MOST LIKELY cause?
Lock Mechanisms and Key Control
8. During the decoding-by-feel activity, a student applies light rotational tension with a tension wrench and then manipulates a pick inside the keyway. Which principle explains why pins can be set one at a time during picking?
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