parallel gears

例句：

1. 1. Thecar's engine has two parallel gears that can be used to change thespeed.
   这辆车的发动机有两个平行齿轮，可以用来改变速度。
2. 2. The machine has threeparallel gears that can be adjusted toincrease or decrease its speed.
   这台机器有三个平行齿轮，可以调整来增加或减少其速度。
3. 3. The gears aremade of high-quality steel and havea smooth operation.
   这些齿轮是用高质量的钢材制成的，操作起来非常平滑。