For use on automatic and semi-automatic machines. Made to highest accuracy standards with all parts hardened and ground. Head opens automatically when the selected thread length is reached. Used with type "D" chasers (style D and DS chasers are interchangeable through 3/4" D) made by Geometric® and other manufacturers. Heads have a special device for roughing and finishing and can be used for cutting over and undersized threads as well as left and right-hand threads.