CPL Lock Installation & Maintenance 2 — Questions and Answers
Question 1: When installing a cylindrical lockset, what is the standard backset measurement used in most US residential applications?
- 1-3/8 inches
- 2-3/8 inches (Correct answer)
- 2-3/4 inches
- 3 inches
Correct answer: 2-3/8 inches
The standard backset for most US residential cylindrical locksets is 2-3/8 inches, measured from the door edge to the center of the bore hole.
Question 2: Which tool is used to cut the edge bore hole for a cylindrical lockset installation?
- Hole saw
- Latch faceplate chisel
- Spade bit (Correct answer)
- Forstner bit
Correct answer: Spade bit
A spade bit is typically used to drill the edge bore (latch hole) in the door edge for cylindrical lockset installation.
Question 3: What is the purpose of a 'strike box' installed behind a door strike plate?
- To reinforce the strike plate mounting screws
- To provide a cavity for the latch bolt to retract into the frame (Correct answer)
- To hold the strike plate in alignment
- To prevent door frame splitting
Correct answer: To provide a cavity for the latch bolt to retract into the frame
A strike box provides a recessed cavity behind the strike plate that allows the latch bolt to fully retract, enabling smooth door operation.
Question 4: When installing a mortise lock, which measurement is critical for ensuring proper operation of the lock body within the door?
- Door width
- Mortise pocket depth (Correct answer)
- Hinge spacing
- Door height
Correct answer: Mortise pocket depth
The mortise pocket depth must exactly match the lock body dimensions to ensure the lock sits flush and operates correctly within the door.
Question 5: What type of lubricant is recommended for maintaining pin tumbler lock cylinders?
- WD-40
- Motor oil
- Graphite powder or dry PTFE lubricant (Correct answer)
- Petroleum jelly
Correct answer: Graphite powder or dry PTFE lubricant
Graphite powder or dry PTFE (Teflon) lubricant is recommended for pin tumbler cylinders because it does not attract dirt or gum up the mechanism.
Question 6: A door latch bolt is not retracting fully when the knob is turned. What is the MOST likely cause?
- Incorrect door backset
- Broken return spring inside the latch mechanism (Correct answer)
- Worn key cuts
- Improper strike plate alignment
Correct answer: Broken return spring inside the latch mechanism
A broken or weakened return spring inside the latch mechanism is the most common cause of incomplete latch retraction when the knob is turned.
Question 7: When installing a surface-mounted rim lock, the screws securing the lock body should be tightened to the door:
- From the exterior side through the lock body
- From the interior side through the back plate (Correct answer)
- Into the door frame jamb
- Into the door edge mortise
Correct answer: From the interior side through the back plate
Rim lock bodies are secured from the interior side through the back plate, ensuring tamper resistance from the exterior.
CPL Lock Installation & Maintenance 2
When installing a cylindrical lockset, what is the standard backset measurement used in most US residential applications?