The file is the most frequently used tool when working with metal, wood, plastics & a host of other materials, so understanding the correct choice and useage of these tools is very important. There are three criteria required to correctly identify a file - the shape (cross-section), the length & the cut. There are many different cross sections available but the principle ones are flat, square, round & half-round. The length of the file is the distance from the sholder below the tang to the end of the file. The cut refers to the patern & density of the teeth.