6. When working with a file, the blades in a vise or against a solid surface such as a work bench to
avoid injury and ensure an even stroke.

When working with a file, stabilize the blade in a vis or against a solid surface such as a work bench to avoid injury and to ensure an even stroke

Explanation:

The file can be used to sharpen a blade to increase the effectiveness of the blade. In order to properly sharpen a file in a safe manner, the blades to be sharpen, which ae usually relatively flexible as compared to the file, should be  made stable during the repetitive forward and backward notion of the file, for safety, to avoid being injured by the recoil of the blade, and also to ensure that the stroke is evenly applied to the blade.