The teeth on a file cut...

The correct answer is that the teeth on a file cut only on a forward stroke. This is a fundamental characteristic of hand files, which are tools designed for shaping, smoothing, and finishing materials, typically metals or woods. When a file is pushed forward, the pointed teeth engage with the material, effectively removing material with each stroke.

During the backward stroke, the file is lifted away from the material, and the design of the teeth prevents them from cutting effectively in that direction. This means that the efficient use of a file relies primarily on the action of pushing it forward, maximizing the cutting potential of the teeth while minimizing wear and resistance during the return stroke.

Understanding this principle is crucial for effective filing techniques, as it helps ensure that users apply the right motions to achieve optimal material removal and workpiece finishing. It also emphasizes proper tool handling and maintenance, as the effectiveness of the teeth is dependent on how the tool is used.