Part 7 of an International Correspondence Schools instruction paper on silk throwing, devoted to combination machines, chiefly the two-process doubler-spinner used to make tram. It covers machine construction and drives, ring rails and cam traverse, spinning rings, travelers and spindles, the stop-motion with drop wires and feed-rolls, twist and speed calculations, production figures, adjustment, oiling, and defects such as hard twist and corkscrew threads. It includes numbered sections with worked rules and examples, tables of traveler weights, twist gear charts and production, engineering drawings, and examination questions at the end.