The 3 to 1 Ratio

When a thread roll has almost reached its maximum penetration, the work on the outside diameter of the part will grow three times for every increment of additional penetration. In other words, if it is determined that a part is being made .003 inches under size, it will only require .001 inches additional die penetration to bring the diameter of the threaded part up to size. This is a very critical adjustment, for if a die penetration is too great, the root area of the roll die threads will be rapidly filled up, causing rapid wear or breakage of the thread roll. The most effective way to control the diameter on the finished part is through careful preparation of the blank.