CPL Pin Tumbler & Cylinder Mechanisms 2 — Questions and Answers
Question 1: What is the purpose of the 'shear line' in a pin tumbler lock?
- It marks where the key blade is cut
- It is the gap between the plug and shell where pins must align to allow rotation (Correct answer)
- It defines the depth of the key cuts
- It separates the driver pins from the key pins
Correct answer: It is the gap between the plug and shell where pins must align to allow rotation
The shear line is the interface between the plug and the shell; when all pin stacks align at this line, the plug can rotate freely.
Question 2: Which component in a pin tumbler cylinder directly contacts the key cuts?
- Driver pins
- Springs
- Key pins (bottom pins) (Correct answer)
- Bible
Correct answer: Key pins (bottom pins)
Key pins, also called bottom pins, rest directly on the key blade and are lifted by the key cuts to different heights.
Question 3: A locksmith discovers a cylinder where the plug spins freely without a key. What is the most likely cause?
- Incorrect key bitting
- All springs are broken or missing (Correct answer)
- The cylinder has been rekeyed incorrectly
- The shear line is too narrow
Correct answer: All springs are broken or missing
If all springs are broken or absent, driver pins cannot drop back to block the shear line, allowing the plug to spin without a key.
Question 4: What does 'master wafer' or 'master pin' refer to in a masterkeyed cylinder?
- An extra-length driver pin used only at the top of the stack
- A small spacer pin inserted between key and driver pins to create an additional shear line (Correct answer)
- A special key pin that works with any key
- A wafer used in place of a coil spring
Correct answer: A small spacer pin inserted between key and driver pins to create an additional shear line
Master pins (also called master wafers) are short pins added between the key pin and driver pin, creating a second shear line that allows a master key to operate the lock.
Question 5: In a standard 6-pin tumbler cylinder, how many pin chambers are present in the plug?
- 3
- 5
- 6 (Correct answer)
- 8
Correct answer: 6
A 6-pin cylinder has six chambers in the plug, each holding one key pin aligned with the corresponding key cut.
Question 6: What is 'bible' in the context of a pin tumbler cylinder?
- The manufacturer's key code manual
- The upper housing of the cylinder shell that contains the driver pins and springs (Correct answer)
- The plug rotation limit stop
- The pin chart showing bitting codes
Correct answer: The upper housing of the cylinder shell that contains the driver pins and springs
The bible (or shell body) is the upper portion of the cylinder housing that retains the driver pins and springs above the plug.
Question 7: Which action during lock picking exploits manufacturing tolerances in a pin tumbler cylinder?
- Raking the key pins up and down rapidly
- Applying rotational tension to bind pins one at a time at the shear line (Correct answer)
- Spraying lubricant to free the plug
- Removing the plug retainer to access pin chambers
Correct answer: Applying rotational tension to bind pins one at a time at the shear line
Single-pin picking applies tension so that manufacturing tolerances cause one pin to bind at the shear line at a time, allowing the picker to set each pin individually.
CPL Pin Tumbler & Cylinder Mechanisms 2
What is the purpose of the 'shear line' in a pin tumbler lock?