This is called an " Allen key" or " hex key" .

这称为“内六角扳手”或“六角扳手”。

And an Allen key or a hex key are really good if you have a bicycle or if you have to undo something or take something apart.

如果您有一辆自行车，或者您必须撤消或拆开某物，那么内六角扳手或六角扳手就非常有用。