Primer on Using Heli Coil® Inserts
BACKGROUND: Heli Coil® inserts are made from 18-8 stainless wire, have a diamond cross section with a hardness of Rc 43-50, an ultimate tensile strength of from 200kpsi to 250kpsi and a surface finish of between 8 and 16 microinches. The final product is larger in diameter than the tapped hole. During installation the insertion tool applies torque to the insert reducing the diameter of the leading coil allowing it to enter the tapped hole. After installation the insert expands outwards with a spring force that permanently anchors the insert in place. The product was invented in the late 1930's to provide a solution for the repair of aircraft engines, especially the threads to attach spark plugs and 'jugs'. The stainless steel insert has a temperature range of from -320F to +800F.
SIZES, TYPES & MATERIALS: There are two designs; the STANDARD which has a free-running thread and the SCREW-LOCK which provides a locking torque on the mating fastener using "chords" on one or more coils of the insert. Available sizes are