There are two styles of Heli-Coil tanged screw thread inserts. The standard or “Free-Running” tanged insert provides a smooth free-running thread, while the “Screw-Locking” tanged insert provides self-locking torque on the male member by a series of “chords” on one or more of the insert coils.
Free-Running tanged screw thread inserts are greater in diameter than the tapped hole into which they are installed. In the assembly operation, the torque applied to the tang reduces the diameter of the leading coil and permits it to enter the tapped thread. When the torque or rotation is stopped, the coils expand with a spring-like action, anchoring the insert permanently in place against the tapped hole.
Screw-Locking tanged screw thread inserts provide an exclusive, resilient internal locking thread that grips the bolt and prevents it from loosening under vibration or impact. Screw-lock inserts permit repeated assembly and disassembly yet will not relax their grip on the screw even in tough metals such as cast iron, alloy steel, titanium, etc.
All tanged screw thread inserts offer savings in space, weight, and money through the elimination of lock wiring, lock nuts, lock washers, chemical compounds, plastic pellets/patches, and other locking mechanisms.
These inserts from Heli-Coil are the original coiled insert and have an extensive background of tension, torque, shear, vibration, and fatigue tests conducted by leading companies as well as the U.S. Military.