The broach for polygonal holes is a specially shaped tool that is fixed to the spindle of the broaching head on one end, while the other end bears the shape of the hole to be obtained. The broaches are manufatured from special HSS steels, duly treated so that they can also be used to machine hard metals. Before starting with the broaching operation, a pre-broach hole must be drilled on the work piece. This pre-broach hole should be a little bit bigger than the shape to machine (from 0,1 to 0,3 mm bigger) and a little bit deeper in order to discharge the chips. It is a good habit of using a good cutting oil during the broaching operation.