FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician is installing a two-piece structural fastener in a highly loaded wing skin joint. The fastener consists of a threaded pin driven through the hole and a collar that is torqued onto the pin's threads until a break-away wrenching feature shears off at a predetermined torque value. Which fastener is being installed?
- AHi-Shear rivet
- BAN standard bolt and nut
- CCherry Max blind rivet
- DHi-Lok fastener
Show answer & explanationAnswer & explanation
Correct answer: D. Hi-Lok fastener
A Hi-Lok fastener consists of a threaded pin and a collar; the collar is torqued onto the pin until the hexagonal wrenching flats shear off at a controlled torque, ensuring consistent clamp-up without needing a torque wrench. It is lighter than a standard bolt while providing high strength.
Why the other options are wrong
- A. A Hi-Shear rivet uses a pin with grooves and a swaged (not threaded/torqued) collar driven with a rivet gun.
- B. A standard AN bolt and nut requires a separate torque wrench and does not have a break-away wrenching feature.
- C. Cherry Max is a blind rivet installed from one side with a pull-mandrel, not a threaded pin-and-collar system.
Hi-Lok Fastener
A two-piece high-strength fastener with a threaded pin and a collar that is torqued until its wrenching flats shear off at a set torque, ensuring proper preload.
- Threaded pin plus collar design
- Collar wrenching flats break away at set torque
- Lighter weight alternative to standard structural bolts
Memory trick: Hi-Lok = collar Locks by breaking off at the right torque.