open gear pair

例句：

1. 1.The new car has a pair of open gears that make it easy to change gears.
   这款新车有一对开放式的齿轮，使得换挡变得很容易。
2. 2. The old man was using an open gear pair to help his grandson learn to ride a bicycle.
   那位老人正在使用一副开放式的齿轮帮助他的孙子学习骑自行车。
3. 3.In the workshop, they used an open gear pair to adjust the tension on the spring.
   在车间里，他们使用一副开放式的齿轮来调整弹簧的张力。