外径

1. Origins, structure, and basic meaning

• Structure: 外径 is read as がいけい and is a noun for the outside diameter of a pipe, ring, or circular form.
• Basic usage: Measuring a pipe’s outside diameter appears in 管の外径を測る, while a ring’s outside diameter being shown appears in 輪の外径が示される.

2. Common pitfalls and similar expressions

• Measurement and drawing notation
  • Use を測る for a physical measurement and が示される for a drawing notation.
• Difference from 内径
  • 外径 measures across outer edges rather than the inner opening.