Threading inserts are replaceable cutting inserts that are used to create internal or external threads. They are used typically with a tool holder on a lathe or turning center.

Threading inserts provide an alternative to thread mills and thread rolling, other methods for creating threads on a workpiece. Like all tools, these replaceable commodities are wear items. 

Types of Threading Inserts

Although some threading inserts have only one cutting surface, others have multiple cutters so that when one tooth wears out, work can move to a sharp tooth. The threading insert’s shape determines the number of sides and cutting angles.

The GlobalSpec SpecSearch database provides information about many different types of threading inserts. Most are described according to shape.

  • Round or circular threading inserts are circular devices used in button mills and radius groove turning. Some are adjustable to employ unused edge portions once part of the edge is worn.
  • Diamond-shaped threading inserts have four sides and two acute angles for thread cutting.
  • Triangular threading inserts have three equal sides and three tips with included angles of 60°. Like other multi-toothed products, they are used with indexable machines.
  • Trigon threading inserts have a modified triangular shape. To allow for higher included angles at the tips, these cutters have bowed sides or intermediate angles on the sides
  • Square threading inserts have square-shaped cutting tips with four equal sides. They are used for precision thread cutting.
  • Rectangular threading inserts have two long sides and short sides. They are used for grooving operations where the short sides contain the actual cutting edge.
  • Rhombic threading inserts and parallelogram threading inserts are also four-sided, but have an angle on the sides for cutting point clearance.
  • Pentagon threading inserts have five equal sides and angles for specific types of thread cutting.
  • Hex or hexagonal threading inserts have six sides.
  • Octagon or octagonal threading inserts are eight-sided and typically indexable for complex cutting operations.

Other types of threading inserts include ball nose, radius tip, and chamfer tip mills. Dogbone threading inserts are available, too. These two-edged inserts have a narrow mounting center and, as their name implies, a broader cutting feature on both ends. They are often used for grooving. 

Thread Types and Insert Size

In addition to the included angle of the tip, thread type is a key specification for threading inserts. Thread type refers to the helical structure used to convert between rotational and linear movement. Common types include UNC, UNRC, UNF, UNRF, 8UN, Acme, and Whitworth threads.

The insert size is generally categorized by the inscribed circle (I.C.), or the diameter of the circle that fits entirely within the insert geometry.  Inscribed circle is used for most indexable inserts, except for rectangular and some parallelogram inserts, where length and width are used.


Main Types of Laydown Inserts

Threading Inserts – Selection Chart