CFS Torque & Tension Specifications 3

Question 1

A fastener specification calls for 'prevailing torque' measurement. What does this assess?

Accepted Answer

The frictional resistance torque of the locking element before clamp load is developed

Answer

Prevailing torque is the resistance offered by the locking feature (e.g., nylon insert, distorted thread) before the fastener engages the joint surface.

Question 2

According to VDI 2230 guidelines, the recommended bolt utilization rate for controlled tightening is approximately:

Accepted Answer

70–90% of proof strength

Answer

VDI 2230 recommends using 70–90% of the fastener's proof strength to maximize clamp load while maintaining a safety margin.

Question 3

What is the effect of increasing the grip length of a bolt on joint stiffness?

Accepted Answer

Decreases joint stiffness

Answer

A longer grip length means a more compliant (less stiff) bolt spring, which improves resilience to dynamic loads but reduces joint stiffness.

Question 4

When converting ft-lb to N·m for a torque specification, which conversion factor is correct?

Accepted Answer

1 ft-lb = 1.356 N·m

Answer

1 ft-lb equals 1.356 N·m; dividing by 1.356 converts N·m back to ft-lb.

Question 5

A torque audit (check torque) is performed after installation. The fastener moves at 95% of the original torque. What does this indicate?

Accepted Answer

The fastener likely has adequate preload within acceptable scatter

Answer

Movement at 90–105% of specification torque during an audit typically indicates acceptable installation; significant shortfall suggests relaxation or improper initial torque.

(CFS) Certified Fastener Specialist Practice Test

(CFS) Certified Fastener Specialist Practice Test

CFS Torque & Tension Specifications 3