Definition
A threaded insert, also known as a threaded bushing, is a fastener element that is inserted into an object to add a threaded hole. They may be used to repair a stripped threaded hole, provide a durable threaded hole in a soft material, place a thread on a material too thin to accept it, mold or cast threads into a workpiece thereby eliminating a machining operation, or simplify changeover from unified to metric threads or vice versa.
Types
Thread repair inserts come in many varieties, depending on the application.
Helical insert
Helical inserts, more commonly known by the trademark Heli-coil, are inserts made of coiled wire. The insert is inserted into a tapped hole that is larger than the desired hole. They are usually over-sized so that they anchor themselves. Some have tangs to install them while others don't. Special tools are required to install the inserts.