CFS Torque & Tension Specifications 2 — Questions and Answers
Question 1: What is the primary purpose of applying torque to a fastener?
- To prevent corrosion under the head
- To develop clamp load (tension) in the joint (Correct answer)
- To seat the thread form into the nut
- To reduce vibration during installation
Correct answer: To develop clamp load (tension) in the joint
Torque is the input; the goal is to generate clamp load (tension) that keeps the joint together.
Question 2: Approximately what percentage of applied torque is typically consumed by friction under the bolt head or nut face?
- 10%
- 25%
- 50% (Correct answer)
- 75%
Correct answer: 50%
Roughly 50% of torque is lost to bearing-surface friction, 40% to thread friction, and only about 10% creates bolt tension.
Question 3: Which fastener property most directly determines the relationship between torque and clamp load?
- Grip length
- Nut factor (K) (Correct answer)
- Thread pitch
- Head height
Correct answer: Nut factor (K)
The nut factor K encapsulates friction and geometry effects, making T = K × D × F the standard torque formula.
Question 4: A grade 8 bolt and a grade 5 bolt of the same size are torqued to the same value. Which statement is correct?
- They develop the same clamp load
- The grade 8 develops higher clamp load due to higher yield strength (Correct answer)
- The grade 5 develops higher clamp load due to better ductility
- Clamp load depends only on thread pitch, not grade
Correct answer: The grade 8 develops higher clamp load due to higher yield strength
Higher-grade bolts have higher proof strength, so the same torque keeps them below yield while stretching them more elastically to develop greater tension.
Question 5: What does 'torque-to-yield' (TTY) installation mean?
- Torquing until the wrench slips
- Intentionally stretching the bolt beyond its elastic limit for higher clamp load (Correct answer)
- Applying torque until the nut face yields
- Using yield-point lubricant during installation
Correct answer: Intentionally stretching the bolt beyond its elastic limit for higher clamp load
TTY fasteners are deliberately torqued past the elastic range to achieve consistent, high clamp load; they must be replaced after disassembly.
Question 6: When a torque wrench is used on an extension that adds length to the drive, what happens to the actual torque applied at the fastener?
- It remains the same
- It increases proportionally to extension length
- It decreases unless a correction is applied (Correct answer)
- It doubles for every inch of extension
Correct answer: It decreases unless a correction is applied
A rigid in-line extension changes the effective lever arm and requires a correction factor to deliver the intended torque at the fastener.
Question 7: Which condition causes the greatest scatter (variability) in the torque-tension relationship?
- Using a calibrated torque wrench
- Dry, unlubricated threads (Correct answer)
- Using ISO-grade nuts with matching bolts
- Consistent operator technique
Correct answer: Dry, unlubricated threads
Dry threads produce high and erratic friction coefficients, often causing ±30–40% variation in resulting clamp load for a given torque.
CFS Torque & Tension Specifications 2
What is the primary purpose of applying torque to a fastener?