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Material code DD in an AN bolt part number

Aviation Mechanic General (AMG) practice question 7 of 33 on Aircraft Materials, Hardware, and Processes. ACS element AM.I.E.K11 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONIn the bolt part number AN3DD5A, what does the letter group DD indicate?

  1. A2024 aluminum alloy
  2. BCorrosion-resistant steel
  3. CCadmium-plated steel with a drilled head
Show the answer and explanation

Correct answer: A. 2024 aluminum alloy

  • A — correct In the handbook's example, the DD in AN3DD5A indicates that the bolt material is 2024 aluminum alloy.
  • B — incorrect The letter C in place of the DD would indicate corrosion-resistant steel.
  • C — incorrect The absence of material letters indicates cadmium-plated steel, and a drilled head is shown by the letter H preceding the length number.

BACKGROUND

AN bolts can be identified by their part numbers as well as by head markings. In the example AN3DD5A, AN designates an Air Force-Navy standard bolt and the 3 indicates the diameter in sixteenths of an inch (3/16). The DD indicates the material is 2024 aluminum alloy; a C in its place would indicate corrosion-resistant steel, and the absence of letters would indicate cadmium-plated steel. The 5 indicates the length in eighths of an inch (5/8), and the A indicates the shank is undrilled. If the letter H preceded the 5 in addition to the A following it, the head would be drilled for safetying.

STUDY TIP

Practice decoding a full AN bolt number field by field, noting that bolt diameter is in sixteenths and bolt length in eighths.

KEY POINTS

  • DD in an AN bolt number means 2024 aluminum alloy.
  • C means corrosion-resistant steel; no letters means cadmium-plated steel.
  • AN3DD5A is a 3/16-inch diameter, 5/8-inch long, undrilled-shank bolt.

SOURCES

  • FAA-H-8083-30B ch07 "Identification and Coding" (bolts, example AN3DD5A)
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.