FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesMedium
A mechanic needs to order a bolt for a critical structural application requiring closer manufacturing tolerances and higher strength than a standard AN bolt provides. Which specification system should the mechanic select?
- AASTM commercial-grade standard
- BSAE J-number standard
- CNAS (National Aerospace Standard)
- DAN (Air Force-Navy) standard
Show answer & explanationAnswer & explanation
Correct answer: C. NAS (National Aerospace Standard)
NAS bolts are manufactured to closer tolerances and often higher strength levels than standard AN bolts, and are used in critical structural applications where precise fit and higher load capability are required. AN hardware is general-purpose aviation hardware with standard tolerances.
Why the other options are wrong
- A. ASTM commercial-grade hardware is not certified for critical aircraft structural use.
- B. SAE J-numbers designate automotive/industrial standards, not aerospace-grade fasteners.
- D. AN hardware has standard (looser) tolerances compared to NAS parts.
NAS Fasteners
National Aerospace Standard hardware manufactured to closer tolerances and higher strength than standard AN hardware, used in critical structural applications.
- NAS = tighter tolerances than AN
- Often used in high-load, critical joints
- MS (Military Standard) parts often replaced AN designations for standardized simplified hardware
Memory trick: NAS = 'Narrow And Snug' tolerances for critical joints