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Rivet diameter from skin thickness

Aviation Mechanic Airframe (AMA) practice question 14 of 20 on Metallic Structures. ACS element AM.II.A.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONUsing the general rule based on skin thickness, what rivet diameter should be selected for a repair to skin that is 0.051 inch thick?

  1. A1/8 inch (0.125 inch)
  2. B5/32 inch (0.156 inch)
  3. C3/16 inch (0.1875 inch)
Show the answer and explanation

Correct answer: B. 5/32 inch (0.156 inch)

  • A — incorrect At 0.125 inch this is smaller than the 0.153 inch figure the rule produces, so it is not the next larger size.
  • B — correct Three times 0.051 inch is 0.153 inch, and the next larger standard rivet diameter above that figure is 5/32 inch, or 0.156 inch.
  • C — incorrect This skips over 5/32 inch; the rule calls for the next larger standard size above the calculated figure, not the one beyond it.

BACKGROUND

Rivet size for a repair is normally taken from the rivets the manufacturer used in the next parallel rivet row inboard on the wing or forward on the fuselage. Where that reference is not available, the handbook gives a general rule: multiply the thickness of the skin by three and use the next larger standard rivet size corresponding to that figure. The worked example in the text uses a skin thickness of 0.040 inch, which gives 0.120 inch and calls for a 1/8 inch (0.125 inch) rivet. The standard diameters that the rule selects from are 3/32, 1/8, 5/32, 3/16, and 1/4 inch. Choosing correctly matters in both directions, because an excessively large rivet in thin material bulges the sheet around the head, while an excessively small rivet in thick material does not provide enough shear strength.

STUDY TIP

Practice the multiply-by-three rule until the arithmetic is automatic, and keep the list of standard rivet diameters and their decimal equivalents in memory.

KEY POINTS

  • Multiply skin thickness by three, then choose the next larger standard rivet diameter.
  • 0.051 inch of skin gives 0.153 inch, which rounds up to a 5/32 inch rivet.
  • A rivet too large bulges thin sheet; one too small lacks shear strength.

SOURCES

  • sources/ama-airframe/ch04.txt "Maintaining Original Strength"
  • sources/ama-airframe/ch04.txt "Drilling" (drill sizes for standard rivets)
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.