Indexable thread mills rotate on a milling machine spindle to form internal or external threads on a workpiece. They have a round shank that mounts to the spindle and a cutting head that accepts compatible multitooth inserts to cut threads to a specific thread standard and pitch. The inserts can be replaced with new ones of the same type or different types without removing the toolholder or tool body from the machine. Indexable threading tools require fewer tool changes than solid tools in high-volume metalworking and fabrication applications with high speeds, high feeds, and difficult-to-machine materials.