The heel is where the file begins to taper into the tang the part the handle goes on. Match the file's shape to the work. Files are shaped to be round, half-round, square, flat or triangular. On the other hand, if the work area requires a gentle curve, a half-round file is ideal. Square files work well for inside 90 degree corners, and round files are made for smoothing round holes.
Flat files are good all-purpose files for any flat, straight edge.
Use a single-cut file when shaping or smoothing ferrous metals. Look for a double-cut file for projects that need material removed and don't require a smooth finish. Consider a file with curved teeth for removing material with a smooth finish. Brass, aluminum and other nonferrous materials are best for this type of file. Inc. How things get done.