Thread repair insert (Heli-Coil)

Maker standard; dimensions align with NASM8846 and ANSI B18.29.1

Sizes

M2-M39 metric, #0-80 upward in inch; length usually 1x to 3x the thread size

Drive & head

Fitted with a tang tool; the finished thread takes a normal screw

Materials

18-8 stainless wire, phosphor bronze, Inconel

Strength / grades

Free running or self-locking types

Hole and pilot guidance

Drill the special insert size (larger than a normal tap drill), tap with the matching STI tap, then wind the insert just below the surface.

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Stripped threads in aluminium engine and gearbox housings

Restores a soft-metal thread to roughly steel strength

Aerospace and high-cycle assemblies

Designed in from new where a soft-metal thread will be undone many times

A standard tap will not work - the insert needs its own oversize tap.
The break-off tang must be retrieved or it rattles around inside the machine.
A short insert in soft metal will pull out - match insert length to the material.