To prevent undo wear, pressure should be applied to a file only on which stroke?

The correct answer is that pressure should only be applied to the forward stroke when using a file. This practice is crucial because the primary function of a file is to cut material as it moves in the forward direction. By applying pressure during this stroke, you encourage the cutting action of the file’s teeth, which are designed to remove material effectively in that direction.

When pressure is applied on the backward stroke, it can blunt the teeth of the file, reducing its effectiveness and leading to premature wear. The design of files is such that the cutting edges work best when moving forward, creating a more efficient cutting action and helping to maintain the longevity of the tool. Additionally, pressure should not be applied during a side or diagonal stroke as these are not standard using techniques for files, and they can lead to damage to both the file and the workpiece.