Most automatic screw machines have trehkanatnoy the self-centering, which is easy to fix the workpiece cylindrical or hexagonal shape. And if it is of square section! In this case, a simple fixture, which is a clamp bushing of soft metal cylinder with a flange in the center of which done square hole and side — notch. Powerlevels Hole first, and then had a file to square shape. The cut made by the hacksaw. If you intend to process billets of different cross sections, it is possible to provide a second slot (shown dotted) below the bushing was split.