FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician is preparing to install standard flush (countersunk head) rivets in an aircraft skin panel. What countersink head angle is standard for these flush rivets?
- A120 degrees
- B82 degrees
- C90 degrees
- D100 degrees
Show answer & explanationAnswer & explanation
Correct answer: D. 100 degrees
Standard flush rivets such as the MS20426 series are manufactured with a 100-degree countersunk head angle, and the countersink or dimple in the sheet must match this angle for a proper flush fit.
Why the other options are wrong
- A. 120 degrees would leave the head sitting too shallow and is not standard.
- B. 82 degrees is the standard angle for AN470 universal (protruding) rivet heads, not flush rivets.
- C. 90 degrees is not a standard aircraft flush rivet head angle.
Flush Rivet Countersink Angle
The standard head angle for countersunk aircraft rivets (e.g., MS20426) that must match the countersink or dimple angle in the skin for proper flush installation.
- Standard flush rivet angle is 100 degrees
- Must match countersink/dimple angle in sheet
- Used to reduce aerodynamic drag on skin surfaces
- Contrasts with 82-degree universal (protruding) head angle
Memory trick: Flush needs 100 to lie flat and smooth.