SkyDrill

Reading a limit dimension

Aviation Mechanic General (AMG) practice question 5 of 15 on Aircraft Drawings. ACS element AM.I.B.K2 · 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 drawing gives a dimension as two stacked figures, 2.01 over 1.99, with no plus or minus sign. What does this express?

  1. AA 2-inch dimension with a total tolerance of only 0.01 inch
  2. BA 2-inch dimension with a plus or minus 0.01 tolerance
  3. CTwo alternative dimensions, either of which is permitted
Show the answer and explanation

Correct answer: B. A 2-inch dimension with a plus or minus 0.01 tolerance

  • A — incorrect The limits 2.01 and 1.99 are 0.02 apart, so the total tolerance is 0.02, which corresponds to plus or minus 0.01.
  • B — correct Instead of plus and minus signs, many drawings give the complete dimension for both tolerances; 2 inches with a plus or minus tolerance of 0.01 is shown as 2.01 over 1.99.
  • C — incorrect The two figures are the upper and lower limits of one dimension, not a choice between two sizes.

BACKGROUND

Drawings may be dimensioned in decimals or fractions, and this is especially true of tolerances. Instead of using plus and minus signs, many figures give the complete dimension for both tolerances. The handbook's example is a 2-inch dimension with a plus or minus tolerance of 0.01, which is shown as 2.01 over 1.99. Dimensions are indicated with or without the inch mark; if no inch mark is used, the dimension is in inches. Reading these limits correctly is part of determining whether a part conforms to its drawing.

STUDY TIP

When you see two stacked figures, treat them as the maximum and minimum limits and work back to the nominal size and tolerance.

KEY POINTS

  • Some drawings show the upper and lower limit dimensions instead of plus and minus signs.
  • 2.01 over 1.99 means 2 inches plus or minus 0.01.
  • Dimensions without an inch mark are in inches.

SOURCES

  • FAA-H-8083-30B ch04 "Reading and Interpreting Drawings"
Practice the Aviation Mechanic General (AMG) test →Timed 60-question exam, by ACS area, or review your misses. Free.
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.