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Torque wrench reading with a drive-end extension

Aviation Mechanic General (AMG) practice question 16 of 33 on Aircraft Materials, Hardware, and Processes. ACS element AM.I.E.K8 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA torque wrench has a lever length of 10 inches. A drive-end extension increases the lever length to 12 inches. To apply 360 inch-pounds to a bolt, what torque should be read on the wrench?

  1. A432 inch-pounds
  2. B300 inch-pounds
  3. C360 inch-pounds, since the extension has no effect
Show the answer and explanation

Correct answer: B. 300 inch-pounds

  • A — incorrect This applies the ratio backwards (360 × 12 ÷ 10). The extension increases the torque delivered, so the wrench reading must be lower than the required torque.
  • B — correct Using Tw = Te × A ÷ B, the wrench reading is 360 × 10 ÷ 12 = 300 inch-pounds.
  • C — incorrect A drive-end extension changes the dial reading needed on any type of torque wrench, so the formula is mandatory.

BACKGROUND

Torque is force times lever length (F × L = T), with the force applied at 90 degrees to the lever. The use of a drive-end extension on any type of torque wrench makes the correction formula mandatory: Tw = Te × A ÷ B, where Tw is the torque reading on the wrench dial, Te is the required torque on the bolt, A is the lever length of the wrench, and B is the lever length of the wrench plus the extension. The force must be applied to the handle at the point from which the measurements were taken, or the torque obtained is incorrect. A handle-length extension alone has no effect on the reading of rigid frame or ratchet wrenches, but it is not advisable on a flexible beam wrench.

STUDY TIP

Set up the formula with A over B; because the extension makes B larger than A, the wrench reading is always less than the target torque.

KEY POINTS

  • With a drive-end extension, wrench reading Tw = Te × A ÷ B.
  • A is the wrench lever length; B is wrench plus extension length.
  • Apply force at the point on the handle from which the lengths were measured.

SOURCES

  • FAA-H-8083-30B ch07 "Torque Wrenches"
  • FAA-H-8083-30B ch07 Figure 7-33 formula text
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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.