rotary mechanism

例句：

1. 1. The car has arotary dial for the speedometer.
   这辆车有一个旋转式的速度表。
2. 2. The machinehas a rotary valve for controlling oilflow.
   这台机器有一个旋转式阀门来控制油流。
3. 3. The gears onthe rotary saw are easy to change.
   旋转锯上的齿轮很容易更换。