FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesEasy
A technician selects an AN fluid line fitting marked with a dash number of '-6.' Based on standard AN numbering, what is the approximate tubing outside diameter?
- A3/16 inch
- B3/4 inch
- C6/8 inch
- D3/8 inch
Show answer & explanationAnswer & explanation
Correct answer: D. 3/8 inch
AN dash numbers indicate tubing outside diameter in sixteenths of an inch. A -6 fitting equals 6/16 inch, which reduces to 3/8 inch.
Why the other options are wrong
- A. Confuses the dash number with an eighths-based system.
- B. Incorrectly doubles the dash number value.
- C. Not a standard reduced fraction and mathematically incorrect.
AN Dash Number Sizing
AN fitting and tubing dash numbers represent the outside diameter of the tube in sixteenths of an inch.
- Dash number ÷ 16 = OD in inches
- -4 = 1/4 inch, -6 = 3/8 inch, -8 = 1/2 inch
- Used consistently across AN fittings and hose sizing
- Helps technicians quickly identify tube size without measuring
Memory trick: Dash number over sixteen tells you the tube's true size.