A precision coil of stainless or nickel-alloy wire that, once installed in a hole tapped with the matching insert tap, presents a standard internal thread to the screw. It repairs damaged threads and is also designed in from the start in aluminum, magnesium and plastic parts, where it spreads load and stops galling. The installation tang is knocked off with a punch afterward unless the insert is a tangless type.
Stripped the drain plug threads in the pan, so drill it, run the insert tap and put a helical insert in.
Everybody calls it a Heli-Coil whatever the brand, and the insert tap is a special size, not the standard tap one size up.
Also heard as
- Heli-Coil
- wire thread insert
- thread repair insert
Related terms
Thread stripping
Failure where the threads of a nut, tapped hole or bolt shear off instead of the bolt breaking.
Thread engagement
The axial length over which external and internal threads fully overlap, which sets stripping strength.
Galling
Adhesive wear where thread surfaces cold-weld and tear under load, seizing a nut partway down a bolt.
Rivnut
A blind threaded insert crushed into a hole in sheet or tube so a screw can be fitted from one side.