A short mathematical analysis showing that any two four-shaft overshot threadings of the same length can be blended onto eight shafts, and that only two mappings accomplish this. Using a digraph notation that pairs a shaft from draft I with a shaft from draft II, the author works through the twill-order rule of overshot threading in tables. The result is a summary table giving which eight-shaft mapping to use based on the first warp thread of each draft.