Home > Helical Inserts, AKA HeliCoil®, Guide

Helical Inserts, AKA HeliCoil®, Guide


If you’re looking for reliable information on Helical Inserts — also known as helical thread inserts, helical coil inserts, Heli-Coils, HeliCoils®, helical wire inserts, or screw thread inserts (STI) — you've come to the right place. Whether you need insights on the different styles available, installation requirements, material specifications, or any other questions you might have about these threaded inserts fastening solutions, our comprehensive guide has you covered! Here, you'll find expert answers to common queries about Helical Inserts. Dive into our resource to ensure you're making the most informed decisions when sourcing or buying them.

*HeliCoil® is the registered trademark of Stanley Engineered Fastening, recently acquired by Bollhoff. Some products and company names are trademarks™ and/or registered trademarks® of their respective holders and does not imply any affiliation or endorsement by them.


Helical Inserts - Quick Navigation.

  1. What is a helical insert, AKA HeliCoil® Insert?
  2. What are helical inserts used for?
  3. What is the difference between helical and Heli-Coil®?
  4. What is the difference between free-running and locking HeliCoils®?
  5. What are helical inserts common specifications?
  6. What is the difference between inch/imperial and metric HeliCoils®?
  7. What are Mil-Spec Helical Inserts?
  8. How are helical inserts installed?
  9. Is a helical insert, aka Heli-Coil®, a permanent fix?
  10. How does a HeliCoil® stay in place?
  11. What are the disadvantages of HeliCoils®?
  12. What is the advantage of using a helical insert?
  13. How long do Helical Inserts last?
  14. What is the alternative to a Helical Insert, AKA Heli-Coil®?
  15. What is the difference between a helical insert and a Keensert®?
  16. Are helical inserts strong in aluminum?
  17. Do you use Loctite® on helical inserts?


1. What is a helical insert, AKA HeliCoil® Insert?

Helical inserts, also known as HeliCoil inserts, helical coil inserts, helical wire inserts, helical threaded inserts, or screw thread inserts (STI), are precision-engineered fasteners (coils of wire) designed to provide precise and durable internal threads (female threads) for standard-sized male threaded fasteners in materials that may be too soft or prone to wear.


2. What are helical inserts used for?

Helical inserts are commonly used to prevent already tapped holes from stripping and wearing out, to make tapped holes smaller, to repair damaged threads in holes, or to create new threads in materials such as aluminum, magnesium, or plastic. The coil’s width is greater than the tapped hole, and once inserted, the outward pressure secures it in place, providing a strong and reliable fastener.


3. What is the difference between helical and Heli-Coil®?

Heli-Coil® is a popular brand name that is commonly used in the industry to refer to helical inserts (product)—similar to how the popular brand name Kleenex® is used to refer to facial tissues (product). The brand name Heli-Coil®, sometimes referred to as just HeliCoil® in the industry, is a registered trademark of the Böllhoff Group. On October 1, 2021, the Böllhoff Group acquired the global rights to the Heli-Coil® trademark from Stanley Engineered Fastening, a subsidiary of Stanley Black & Decker.


4. What is the difference between free-running and locking HeliCoils®?

Free-running helical inserts feature a smooth and free-running thread. Locking helical inserts share these characteristics but additionally enable frequent removal and reassembly of screws without significant torque loss. They also securely hold threaded fasteners against loosening due to vibration or shock.

Free running is the most common style used for thread repair. The “free” diameter of the insert is larger than the installed diameter and this configuration generates balanced pressure distribution between the coils and threads.


5. What are helical inserts common specifications?

  • Thread Size: The internal diameter and pitch for helical inserts range from #2-56 through 1 ½-6” for inch/imperial sizes, and from M2 through M24 for their metric counterparts.
  • Material: HeliCoils are typically made from Stainless Steel 18-8, Stainless Steel 316, Phosphor Bronze, Nitronic 60 or Inconel for high-temperature applications.
  • Length: Measured in multiples of the thread diameter, usually available in standard lengths like 1D, 1.5D, 2D, and 2.5D. Standard inserts lengths measure from 1x to 3x the diameter. Note: larger sizes may be available by special order.
  • Coating: Options include dry film lubricants or cadmium plating for improved corrosion resistance.
  • Tolerance: Class of fit for the HeliCoil, ensuring precision in the fit and function.
  • Locking Mechanism: Whether the helical insert is free-running or has a locking feature for vibration resistance.
  • Installation Method: Types of tools required for installation, such as manual or power tools.
  • Application: Specific uses, such as aerospace, automotive, or general industrial applications.


6. What is the difference between inch/imperial and metric HeliCoils®?

The primary difference between inch/imperial-sized and metric-sized helical inserts (aka HeliCoils) lies in their measurement systems and thread specifications:

  • Measurement System: Inch/imperial sized helical inserts are measured in inches and follow the United States customary system. Metric sized helical inserts, on the other hand, are measured in millimeters and follow the metric measurement system used globally.
  • Thread Specifications: Inch/imperial-sized helical inserts follow the Unified Thread Standard (UTS), featuring common thread types such as UNC (Unified National Coarse) and UNF (Unified National Fine). In contrast, metric-sized helical inserts adhere to the ISO Metric Thread Standard, with common thread types including coarse and fine metric threads (e.g., M6x1, M10x1.5).
  • Identification: Inch/imperial helical inserts are typically identified by their inch-based thread sizes, such as 1/4-20 or 10-32. Metric helical inserts, on the other hand, are identified by their metric thread sizes, such as M6x1 or M8x1.25 -- where "M" indicates metric, "8" is the nominal diameter in millimeters, and "1.25" is the thread pitch in millimeters.
  • Usage: Inch/imperial helical inserts are commonly used in regions where the imperial system is standard, such as the United States. In contrast, metric helical inserts are widely used internationally and in regions where the metric system is standard.


7. What are Mil-Spec Helical Inserts?

Mil-Spec Helical Inserts (Heli-Coils®) are wire inserts crafted to meet military specifications. They carry specific labels signifying their adherence to the rigorous standards established by the U.S. Department of Defense in order to guarantee that the inserts will fulfill the necessary requirements for military applications.

These threaded inserts often show up as free-running or self-locking inserts under their Mil-spec numbers, which can be crossed to commercial equivalents. Some common Mil-spec series include: MS122076 through MS122275, NAS1130, MS124651 through MS124850, MS21208, MS21209-C & MS21209-F, MS122076, MS33537, MA3279, MA3329, and NA0276 series. Note: All of these offerings are the tanged version of helical inserts.


8. How are helical inserts installed?

  1. Drill the Hole: Use a correctly sized drill bit to drill a hole where the helical insert will be installed.
  2. Tap the Hole: Use a matching tap to create threads in the drilled hole. This step is crucial as it forms the base threads that will hold the helical inserts in place.
  3. Insert the Helical Insert:
    • Place the helical insert onto the installation tool. Align the tang of the insert with the notch on the installation tool.
    • Thread the insert into the tapped hole using the installation tool, applying even pressure. Ensure the insert goes in smoothly and is not cross-threaded.
  4. Set the Insert: Continue threading the insert until it is flush with or slightly below the surface of the material.
  5. Break the Tang: Use a tang break-off tool or a punch to remove the tang at the bottom of the insert. Place the tool into the insert and give it a sharp tap to break the tang off cleanly. This step ensures that the hole remains open and usable for the bolt or screw.
  6. Inspect the Installation: Verify that the insert is properly seated and that the threads are aligned and clean. The insert must be securely in place without any movement.


9. Is a helical insert, aka Heli-Coil®, a permanent fix?

A helical insert, aka Heli-Coil or HeliCoil, is not considered a permanent fix. These inserts are designed to be removable and replaceable, providing a flexible solution for repairing damaged threads or reinforcing threads in softer materials. While they are durable and can last a long time under normal use, they can be removed and replaced if they wear out or if the host material needs rework.

The ability to remove and replace helical inserts also makes them versatile and practical for applications requiring maintenance or future disassembly. Their design allows for easy installation and removal without damaging the parent material.


10. How does a HeliCoil® stay in place?

A helical insert stays in place through a combination of its design and the installation process. Here’s how it works:

  • Coiled Wire Design: A helical insert is a tightly wound helical wire that expands slightly when installed. The outer diameter of the coil is larger than the tapped hole into which it is inserted.
  • Elastic Expansion: When the HeliCoil is threaded into the hole, it compresses slightly. Once installed, the coil expands outward, exerting pressure against the walls of the tapped hole. This outward pressure helps secure the insert in place.
  • Thread Engagement: The internal threads of the Helical Insert engage with the threads of the bolt or screw being used. This engagement helps lock the insert in place and ensures that the load is distributed across the entire length of the insert, enhancing its holding power.
  • Tang Break-Off: During installation, a tang at the end of the HeliCoil is used to drive the insert into the hole. After installation, this tang is broken off, allowing the insert to form a continuous, strong thread.

The combination of these factors—compression during installation, outward pressure, and thread engagement—ensures that a Helical Insert stays securely in place.


11. What are the disadvantages of HeliCoils®?

Helical inserts, aka HeliCoils, have some disadvantages, including higher cost compared to standard fasteners, and the potential for movement/loosening if not installed correctly. Additionally, they may not be suitable for all materials, particularly very soft or brittle ones, and there are limitations on available thread sizes.


12. What is the advantage of using a helical insert?

There are several benefits to using a helical insert, some of them include: providing high-strength threads in softer materials, extending the life of threaded assemblies, and enabling thread repair without needing to replace entire components.


13. How long do Helical Inserts last?

The lifespan of helical inserts, or HeliCoils, largely depends on the application and the conditions they are subjected to. Under normal use in a stable environment, helicoils can last for the lifetime of the component they are installed in, as they are designed to provide durable and strong threads in softer materials. However, in high-stress, high-vibration, or corrosive environments, their lifespan may be shorter, and regular inspections and maintenance might be required to ensure their integrity.


14. What is the alternative to a Helical Insert, AKA Heli-Coil®?

The alternative to a helical insert is its counterpart, the key locking insert—also known in the industry by the popular brand name Keensert! Both “Heli-Coil®” or helical insert and “Keensert®” or Key locking insert fall under the “threaded insert” category of fasteners and sometimes are used interchangeably for some applications.

Here, at MF Supply, we specialize in both Keenserts Style Inserts and Helical inserts for manufacturers, government and industry. Don’t know what a Keensert is? Check out our other guide about Keenserts to learn everything you need to know about this threaded fastener!


15. What is the difference between a helical insert and a Keensert®?

There are three main differences between key locking inserts, aka Keenserts, and helical inserts:

  1. Strength: Key locking inserts are stronger than Helical wire inserts.
  2. Ease of installation: Key locking inserts are easier to install than Helical wire inserts.
  3. Price: Key locking inserts are more expensive than Helical wire inserts.

In heavy wear, high vibration and high heat situations—where saving space is not a concern and hole depth is limited—Key locking inserts are the best bet.

When reducing costs and minimizing space are priorities, helical inserts are the way to go. They are particularly useful for creating permanent strong threads in softer materials such as aluminum, titanium and magnesium alloys, and are best suited to lower heat and lower torque environments.


16. Are helical inserts strong in aluminum?

Yes! They are strong and work well with aluminum, plastic, and other softer materials.

Note: When choosing a helical insert, it’s essential to consider factors like the material you’re working with, the stresses the insert will be under, and the expected lifecycle of the product. Industrial, automotive and aerospace industries each have their own requirements, which may include DFAR, First Article or other certifications.


17. Do you use Loctite® on helical inserts?

Using Loctite on helical inserts is generally not necessary, as the inserts are designed to stay in place through their own tension and the pressure they exert against the threads of the parent material. However, in applications where additional security is required due to high vibration or other stresses, applying a thread-locking adhesive like Loctite can provide extra assurance that the insert will not come loose.

It's also important to select the right type of Loctite, as different grades provide varying levels of strength and removability. For most applications, a medium-strength thread locker, such as Loctite Blue 242, is sufficient. For high-stress environments, a high-strength thread locker, like Loctite Red 271 may be more appropriate, but keep in mind that it will require heat to remove.


We hope you found this resource helpful in addressing your questions about Helical inserts. If you have further inquiries or wish to speak with a representative, please send us an RFQ or contact us directly. Remember, "Finding the right screw for you" is our commitment to you!