CFS Locking & Anti-Vibration Fasteners Flashcards
6 cards from real CFS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CFS Locking & Anti-Vibration Fasteners flashcards as text
A Nord-Lock washer system uses two washers with opposite-direction cams. How does this system prevent loosening?
Answer: The cam geometry forces the bolt to tighten further if rotation is attempted, since the rise of the cams exceeds the thread pitch
Nord-Lock washers have a cam angle greater than the thread pitch angle, so any attempt to rotate the bolt or nut in the loosening direction forces the bolt to elongate further rather than unscrew.
In a vibration-prone joint, which combination is generally considered most effective for critical fastener security?
Answer: Plain nut + anaerobic adhesive (medium strength)
An anaerobic adhesive fills thread voids and cures to a solid polymer, providing continuous resistance to loosening across the entire thread engagement length, making it highly effective in vibration applications when correctly applied.
Per ASTM F959, what are 'direct tension indicators' (DTIs), and how do they indicate proper bolt tension?
Answer: Hardened washers with raised protrusions that flatten to a specified gap when the required bolt tension is achieved
DTI washers per ASTM F959 have small bumps on one face that progressively collapse as bolt tension increases; a feeler gauge checks the remaining gap to confirm the required tension has been achieved.
Which standard governs the performance requirements for prevailing torque hex nuts (all-metal type) in the United States?
Answer: ASME B18.16.6
ASME B18.16.6 covers prevailing torque hex nuts (all-metal type), specifying dimensional requirements and prevailing torque performance for inch-series nuts.
When specifying a locking fastener for a joint subjected to both vibration and elevated temperature (>300°F), the LEAST suitable option is:
Answer: Nylon insert lock nut (Nylock)
Nylon inserts typically begin to soften and lose their locking effectiveness above approximately 250–300°F (121–149°C), making them unsuitable for high-temperature vibration applications.
The primary mechanism by which vibration causes bolt self-loosening (as studied by Gerhard Junker) is:
Answer: Transverse slip at the thread and bearing interfaces that causes incremental rotation of the nut or bolt head
Junker's research established that transverse (lateral) slippage at the thread flanks and bearing face — not axial vibration — is the dominant mechanism by which bolts self-loosen under vibration.