中径是通过螺纹轴向截面内牙型上的沟槽和凸起宽度相等处的假象圆柱的直径（如图中d2）。中径是确定螺纹几何参数和配合性质的直径。
API圆螺纹的锥度和中径是两个重要的参数。
The taper and pitch diameter of API round thread casing are two of the most important parameters.
检测圆锥管螺纹基面中径的方法有很多，但测量过程复杂。
There are many ways to measure base-level pitch diameter of cone-shaped thread.
分析比较了紧密距测量以及中径和椭圆度量规测量的误差。
The errors of the stand-off measurement and measurement errors made by pitch diameter gauge and ovality gauge are analyzed and compared.
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