There are two correct answers to this question which are, A. Allows space for clean bends in metal and B. Indicates where a bend should occur when laying out and marking. This tool would be used by a person who is doing a home improvement job. Professionals and everyday homeowners use hand notchers.
These tools can be found at home improvement stores like Lowes and Home Depot, as well as online stores like Amazon. It is important for the hand notcher to be sharp, so that it can cut through metal. The notcher also includes grips so that it is easy to handle.