Fluid Lines & Fittings

Aircraft rigid tubing is sized by a dash number that states the outside diameter in sixteenths of an inch. What is the outside diameter of a size -6 aluminum tube?

Answer

3/8 inch

Tube OD is expressed in 1/16-inch increments, so a -6 tube is 6/16 inch, which reduces to 3/8 inch. '3/4 inch' comes from mistakenly reading the number as eighths (6/8); '3/16 inch' comes from using a 1/32 base; '6 inches' takes the dash number literally.

Source: FAA-H-8083-30B, Chapter 9, Fluid Lines and Fittings (tubing size/identification)

Not the answer

  • 3/16 inch
  • 3/4 inch
  • 6 inches

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