The axis of a circle is its diameter.

圆的对称中心线就是直径。

《牛津词典》

A diameter passes through the center of a circle.

直径从圆心穿过。

youdao

Abstract: this paper designs a measuring instrument which can measure addendum circle and dedendum circle diameter of odd_tooth gears and can define all main parameters of gears.

文摘：设计了一种测量工具，用以测量奇数齿齿轮的齿顶圆和齿根圆直径，以便确定齿轮的主要参数。

youdao

Using a paring knife, cut the dough into a circle that is 1 inch larger than the diameter of the pan you're using.

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