ballscrew

例句：

1. 1. The car needs anew ballast to fix the engine.
   这辆车需要更换新的平衡块来修理引擎。
2. 2. The bolts holding the door shutwere rusted through.
   固定门的螺栓生锈了，已经锈穿了。
3. 3. The screwdriver was too small for the screwson the wall.
   螺丝刀太小，无法拧紧墙上的螺丝。