A short web document by Ralph Griswold introducing profile tie-ups in profile (block) drafts. It explains how a profile tie-up, such as a 2/2 twill for overshot, shapes the block pattern, and how it is converted to a threading tie-up by block substitution (e.g. 3/1 twill for black cells and 1/3 twill for white). Diagrams show profile tie-ups, substitution rules and the resulting block patterns for sample profile threading and treadling sequences.