The comparator when used to check depth is only as accurate as the skill level of the operator. It is critical that the image is focused sharply, the travels have been calibrated, and the machine is in excellent condition with digital read out capacities to avoid mixed interpretations. The power setting must be at least 20x with the ability to go to 50x if necessary. In the case of shallow angles and intersecting radii, a theoretically sharp corner has to be determined with overlays for the reading to be accurate. With some of the more complex readings a con-trace of the cast is the best choice.

• Parts out of tolerance after heading. If the die isn't thoroughly correct, all aspects of the heading process suffer. Any incorrect dimensions not discovered in the header die will have to be corrected, if possible, by later operations at the screw manufacturer's time and expense.

• Incorrect press fits of inserts assembled in cases. Many die failures are caused by incorrect press fit. Both too much and too little. This is caused by tri-round O.D.s, inaccurate measurement of the parts, and inexperienced Die Makers assuming incorrectly the proper press needed.
• Parts not fitting correctly in subsequent dies in multi-die set ups. It is imperative to make sure that the engineering done in multi-station formers is not undermined by die components that are not exactly to specifications denoted by the engineer.