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Computing tolerance from unequal allowances

Aviation Mechanic General (AMG) practice question 10 of 15 on Aircraft Drawings. ACS element AM.I.B.K3 · 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 print gives a dimension as 0.225 + 0.0025 - 0.0005. What is the tolerance for that dimension?

  1. A0.0020 (0.0025 minus 0.0005)
  2. B0.0050 (twice the plus figure)
  3. C0.0030 (0.0025 plus 0.0005)
Show the answer and explanation

Correct answer: C. 0.0030 (0.0025 plus 0.0005)

  • A — incorrect Subtracting the two allowances does not give tolerance; the definition is the sum of the plus and minus figures.
  • B — incorrect Doubling the plus figure applies only when the allowances are equal, as in 0.225 plus or minus 0.0025; here the minus allowance is smaller.
  • C — correct Tolerance is the sum of the plus and minus allowance figures, so 0.0025 plus 0.0005 equals 0.0030; this is the handbook's own worked example.

BACKGROUND

The plus figure on a dimension gives the maximum allowable variation above the stated size, and the minus figure gives the minimum allowable variation below it. With 0.225 + 0.0025 - 0.0005, the part is acceptable if it is not more than 0.0025 larger or 0.0005 smaller than 0.225. The tolerance is the sum of the two allowances, 0.0025 plus 0.0005, which is 0.0030. Only when the plus and minus allowances are the same, written as plus or minus 0.0025, would the tolerance be 0.0050.

STUDY TIP

Add the two allowance figures regardless of their signs; the signs only tell you which direction each allowance runs.

KEY POINTS

  • 0.225 + 0.0025 - 0.0005 allows up to 0.0025 over and 0.0005 under.
  • Tolerance is 0.0025 plus 0.0005, which equals 0.0030.
  • Doubling the plus figure is valid only for equal plus-or-minus allowances.

SOURCES

  • FAA-H-8083-30B ch04 "Allowances & Tolerances"
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MORE ON AIRCRAFT DRAWINGS

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.