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HELI-COIL

HELI-COIL is a brand of helical thread inserts and associated installation tooling used to repair or reinforce internal threads in metal components. The product line originated with the development of the wire thread insert in the 1930s and has since become a standard reference for thread repair in aerospace, automotive, industrial machinery, and general maintenance work. The core principle is straightforward: a coiled wire insert of diamond-shaped cross-section is installed into a tapped hole using a dedicated STI (screw thread insert) tap, creating a new internal thread that is typically stronger than the original parent material thread. HELI-COIL inserts are available in free-running and screw-locking configurations, with tanged and tangless styles. Free-running inserts allow normal bolt installation and removal; screw-locking inserts include a deformed coil that grips the mating fastener to resist vibration-induced loosening. Tangless versions eliminate the tang that must otherwise be broken off and retrieved after installation, which reduces the risk of foreign object debris in critical assemblies. Materials include 18-8 stainless steel and Nitronic 60, with tensile strengths commonly cited in the 200,000 to 250,000 psi range. Thread sizes span inch and metric, coarse and fine pitches, from small machine screws through larger UNF and metric sizes. 3G Electric supplies the HELI-COIL line as part of its industrial equipment catalog, covering inserts, STI taps, installation tools, extraction tools, and kits. The range includes individual inserts in pack quantities, prewinder-type installation tools, and complete thread repair kits that bundle inserts, drill, tap, and installation tool for a specific thread size. STI taps are offered in straight-flute and spiral-flute configurations with class of fit and thread limit designations such as H4 / 3B. Because thread repair often occurs during maintenance or rework, having the correct insert style, material, and tooling on hand matters more than brand promotion. 3G Electric lists HELI-COIL SKUs with specifications including thread size, thread type, material, finish, tensile strength, and pack quantity, so buyers can match the insert to the parent material and service condition. The catalog covers both the consumable inserts and the tooling needed to install and remove them, which supports planned maintenance and unplanned repair situations across plants that maintain threaded assemblies in metal housings, castings, and machined components.

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About HELI-COIL

HELI-COIL is a brand of helical thread inserts and associated installation tooling used to repair or reinforce internal threads in metal components. The product line originated with the development of the wire thread insert in the 1930s and has since become a standard reference for thread repair in aerospace, automotive, industrial machinery, and general maintenance work. The core principle is straightforward: a coiled wire insert of diamond-shaped cross-section is installed into a tapped hole using a dedicated STI (screw thread insert) tap, creating a new internal thread that is typically stronger than the original parent material thread. HELI-COIL inserts are available in free-running and screw-locking configurations, with tanged and tangless styles. Free-running inserts allow normal bolt installation and removal; screw-locking inserts include a deformed coil that grips the mating fastener to resist vibration-induced loosening. Tangless versions eliminate the tang that must otherwise be broken off and retrieved after installation, which reduces the risk of foreign object debris in critical assemblies. Materials include 18-8 stainless steel and Nitronic 60, with tensile strengths commonly cited in the 200,000 to 250,000 psi range. Thread sizes span inch and metric, coarse and fine pitches, from small machine screws through larger UNF and metric sizes. 3G Electric supplies the HELI-COIL line as part of its industrial equipment catalog, covering inserts, STI taps, installation tools, extraction tools, and kits. The range includes individual inserts in pack quantities, prewinder-type installation tools, and complete thread repair kits that bundle inserts, drill, tap, and installation tool for a specific thread size. STI taps are offered in straight-flute and spiral-flute configurations with class of fit and thread limit designations such as H4 / 3B. Because thread repair often occurs during maintenance or rework, having the correct insert style, material, and tooling on hand matters more than brand promotion. 3G Electric lists HELI-COIL SKUs with specifications including thread size, thread type, material, finish, tensile strength, and pack quantity, so buyers can match the insert to the parent material and service condition. The catalog covers both the consumable inserts and the tooling needed to install and remove them, which supports planned maintenance and unplanned repair situations across plants that maintain threaded assemblies in metal housings, castings, and machined components.

Common Applications

  • Aerospace — Tangless screw-locking HELI-COIL inserts in 18-8 stainless steel for vibration-resistant threaded joints in airframe and engine components.
  • Automotive — Free-running tanged HELI-COIL inserts in metric sizes for repairing stripped threads in aluminum engine blocks and transmission housings.
  • Industrial machinery — STI taps and prewinder installation tools for on-site repair of threaded holes in cast iron and steel machine frames.
  • Oil and gas — Nitronic 60 HELI-COIL inserts for galling resistance in stainless steel valve bodies and pump housings exposed to corrosive media.
  • MRO and maintenance — HELI-COIL thread repair kits containing inserts, drill, tap, and installation tool for restoring damaged threads without replacing the parent component.
  • Electrical equipment — Screw-locking tangless HELI-COIL inserts for securing fasteners in metal enclosures and control panels subject to vibration.

Frequently asked questions

Common questions about HELI-COIL from 3G Electric.

What is the difference between free-running and screw-locking HELI-COIL inserts?

Free-running HELI-COIL inserts provide a standard internal thread that allows the mating fastener to be installed and removed without added resistance. Screw-locking inserts have one or more coils deformed inward, which creates interference with the fastener threads and increases resistance to vibration loosening. Screw-locking inserts are typically specified where the joint experiences dynamic loading or where a locking feature is required. Both styles are available in tanged and tangless configurations and in materials such as 18-8 stainless steel and Nitronic 60.

What does tangless mean on a HELI-COIL insert?

A tang is a small driving protrusion on the end of a tanged insert that engages the installation tool. After installation, the tang must be broken off and removed. Tangless HELI-COIL inserts are installed with a tool that drives the insert without a tang, so no break-off or retrieval step is required. This reduces the risk of leaving a loose tang inside a closed cavity or assembly. Tangless inserts are often selected for applications where foreign object debris is a concern, such as in fuel, hydraulic, or pneumatic systems.

What STI tap do I need for a HELI-COIL insert?

HELI-COIL inserts require a screw thread insert (STI) tap, which cuts a larger internal thread than the nominal fastener size to accommodate the insert. The STI tap size corresponds to the insert thread size and pitch. For example, a #10-32 insert uses a #10-32 STI tap. Taps are specified with class of fit and thread limit, such as H4 / 3B, and may be straight-flute or spiral-flute depending on the material and hole type. The tap must match the insert thread size, pitch, and tolerance class to ensure correct installed thread dimensions.

What materials are HELI-COIL inserts available in?

HELI-COIL inserts are commonly supplied in 18-8 stainless steel and Nitronic 60. 18-8 stainless steel provides corrosion resistance and is suitable for general industrial use. Nitronic 60 is a galling-resistant stainless steel often selected for applications where the mating fastener is stainless steel and galling is a concern, or where higher temperature or wear resistance is needed. Tensile strengths for these inserts are typically in the 200,000 to 250,000 psi range. Other materials may be available depending on the specific part number and thread size.

How do I remove a damaged HELI-COIL insert?

Removal of a damaged HELI-COIL insert is done with an extraction tool designed for the insert style and thread size. The extraction tool engages the insert and allows it to be unscrewed or pulled from the hole. For tanged inserts, the extraction tool typically has a cutting edge that grips the insert's internal thread. For tangless inserts, a specific extraction tool is used. After removal, the hole can be inspected and, if the threads are still serviceable, a new insert can be installed. If the hole is damaged, it may need to be retapped or repaired before installing a new insert.

What is included in a HELI-COIL thread repair kit?

A HELI-COIL thread repair kit typically includes a quantity of helical inserts for a specific thread size, the corresponding STI tap, a drill bit for the STI tap, and an installation tool. Some kits also include an extraction tool. The kit format provides the consumable inserts and the tooling needed to complete a repair in one package. Kit contents vary by part number and thread size. For example, a kit for #10-32 fine threads would include #10-32 inserts, a #10-32 STI tap, the specified drill, and an installation tool for that insert size.