CFS CFS Locking & Anti-Vibration Fasteners 2 — Questions and Answers
Question 1: A castle nut (castellated nut) with a cotter pin provides locking by:
- Friction between the nut and bearing surface
- Positive mechanical restraint — the cotter pin through the bolt hole prevents nut rotation regardless of clamp load (Correct answer)
- Chemical bonding of threads
- Elastic deformation of the nut crown
Correct answer: Positive mechanical restraint — the cotter pin through the bolt hole prevents nut rotation regardless of clamp load
The cotter pin passes through slots in the castle nut and a cross-drilled hole in the bolt, creating a positive mechanical lock that prevents rotation even under complete loss of preload.
Question 2: Thread-locking adhesives (e.g., anaerobic adhesives like Loctite) cure in the absence of air and presence of metal ions. What property distinguishes a 'medium strength' grade from a 'high strength' grade?
- Medium strength cures faster; high strength requires heat to cure
- Medium strength allows disassembly with standard hand tools; high strength typically requires heat or special tools for removal (Correct answer)
- Medium strength is used only on stainless steel; high strength is for carbon steel
- Medium strength is blue; high strength is always red
Correct answer: Medium strength allows disassembly with standard hand tools; high strength typically requires heat or special tools for removal
Medium-strength (typically blue) anaerobic adhesives are designed to be disassembled with standard tools, while high-strength (typically red) grades require heat application or significant force to break the bond.
Question 3: Which type of serrated flange fastener provides locking action by biting into the mating surface upon tightening?
- Plain flange nut
- Serrated (tooth) flange nut (Correct answer)
- Heavy hex nut
- Jam nut
Correct answer: Serrated (tooth) flange nut
Serrated flange nuts have radial teeth on the flange bearing surface that bite into the mating material when torqued, creating mechanical locking resistance against vibration-induced loosening.
Question 4: A jam nut (thin nut) used as a locking method works by:
- Compressing the bolt threads between the two nuts, creating a locked friction grip (Correct answer)
- Acting as a spring to maintain preload
- Chemically bonding to the primary nut
- Providing a positive mechanical stop against rotation
Correct answer: Compressing the bolt threads between the two nuts, creating a locked friction grip
When a jam nut is tightened against a primary nut, the bolt is placed in tension between them and the threads are loaded in opposite directions, creating high friction that resists self-loosening.
Question 5: Wiring (safety wiring) of fasteners is a positive locking method most commonly required in which industry?
- Consumer electronics
- Aerospace and military aviation (Correct answer)
- Residential construction
- Plastic injection molding
Correct answer: Aerospace and military aviation
Safety wiring is mandated in aerospace and military aviation (per MIL-DTL-83519 and AC 43.13) to provide positive locking for critical fasteners that cannot be allowed to loosen in flight.
Question 6: What is the correct direction to route safety wire between two fasteners to ensure the wire tensions both fasteners in the tightening direction?
- Wire runs straight between fasteners with no tension requirement
- Wire is routed so that any loosening tendency in either fastener pulls the wire taut and tensions the adjacent fastener toward tightening (Correct answer)
- Wire is routed in the loosening direction so it acts as a fuse
- Direction does not matter as long as both fasteners are wired
Correct answer: Wire is routed so that any loosening tendency in either fastener pulls the wire taut and tensions the adjacent fastener toward tightening
Safety wire must be routed so that the pull on the wire — if either fastener begins to loosen — applies a tightening torque to that fastener, providing active locking restraint.
CFS CFS Locking & Anti-Vibration Fasteners 2
A castle nut (castellated nut) with a cotter pin provides locking by: