Made of micrograin carbide, thread mills and insert mills produce threads that achieve tight, leak-free joints in petroleum and gas pipe. Spiral-fluted thread mills produce NPT/API thread dia from 1/16-2 in. Indexable partial-profile insert thread mills cut NPT/API thread dia from 1-20 in. Solid thread mills have free-cutting geometry; each indexable insert has 4 usable cutting edges.