radius bar

例句：

1. 1. The radius bar is used to measure the distance between two points on a circle.
   半径棒用于测量圆上两点之间的距离。
2. 2. The radius bar was used to mark the center of the circle.
   用半径棒标记圆心。
3. 3. The radius bar was used to measure the length of the radius.
   用半径棒测量半径的长度。