CFS CFS Locking & Anti-Vibration Fasteners

Question 1

Which of the following best describes the locking mechanism of a prevailing torque nut (e.g., nylon insert lock nut)?

Accepted Answer

It creates friction through a deformed or non-metallic insert that grips the bolt threads independent of clamping load

Answer

Prevailing torque nuts create a mechanical interference fit — through a nylon insert or deformed metal threads — that resists rotation independent of the joint's clamp load.

Question 2

A Belleville (conical spring) washer used as a locking device primarily functions by:

Accepted Answer

Maintaining a residual spring load that compensates for minor clamp load loss due to embedding or relaxation

Answer

Belleville washers act as spring elements that store elastic energy, compensating for small losses in joint preload caused by embedding relaxation or thermal cycling.

Question 3

Per IFI and industry standards, a nylon insert lock nut (Nylock) should generally NOT be reused after removal because:

Accepted Answer

The nylon insert permanently deforms and loses its interference fit after the first installation

Answer

The nylon insert deforms to match the bolt thread profile during initial installation; upon removal and reinstallation, the insert no longer provides consistent interference, reducing its locking effectiveness.

Question 4

What is the primary difference between free-spinning lock washers and prevailing torque fasteners in a joint assembly?

Accepted Answer

Prevailing torque fasteners create locking resistance throughout tightening and loosening, while free-spinning lock washers only function under clamp load

Answer

Prevailing torque fasteners resist rotation at all times due to mechanical interference, whereas split or toothed lock washers rely on clamp load to bite into surfaces and lose effectiveness if clamp load drops.

Question 5

Which fastener locking method is considered most reliable in high-temperature environments where nylon inserts would degrade?

Accepted Answer

All-metal prevailing torque nut (distorted thread or beam-type)

Answer

All-metal prevailing torque nuts (e.g., ESNA or distorted-thread designs) maintain their locking function at elevated temperatures where nylon degrades and most thread-locking adhesives lose effectiveness.

(CFS) Certified Fastener Specialist Practice Test

(CFS) Certified Fastener Specialist Practice Test

CFS CFS Locking & Anti-Vibration Fasteners