FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesMedium
A technician uses a metric caliper and measures a tube's outside diameter as 12.7 mm. Using 1 inch = 25.4 mm, what is this diameter in inches?
- A1.270 inches
- B0.250 inch
- C0.500 inch
- D5.000 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 0.500 inch
Dividing 12.7 mm by 25.4 mm/inch gives 0.500 inch. This confirms the tube matches a standard 1/2-inch aircraft tubing size.
Why the other options are wrong
- A. This confuses the millimeter reading with the inch answer.
- B. This is half the correct value, from a math error.
- D. This results from multiplying instead of dividing.
Metric-to-English Length Conversion
Converting millimeter measurements to inches by dividing by the conversion factor 25.4 mm per inch.
- 1 inch = 25.4 mm exactly
- Divide mm by 25.4 to get inches
- Multiply inches by 25.4 to get mm
Memory trick: '25.4 is the magic gate' between inches and millimeters.