A helicoil insert is one of the easiest and most reliable ways to fix stripped or damaged threads without replacing the whole part. Thread damage is common in cars, machines, tools, and equipment that are taken apart and put back together many times. When threads fail, repairs can become expensive and time-consuming.
A helicoil insert solves this problem by restoring the original thread size and often making it stronger than before. In this guide, we explain what a helicoil insert is, how it works, where it is used, and how to install it correctly.
Understanding these components is key for any maintenance or engineering team looking to maintain structural integrity in soft materials. Proper repair techniques save time and prevent the need for costly part replacements.
What Is a Helicoil Insert and How Does It Work?
A helicoil insert, also called a helical thread insert, is a tightly wound stainless steel wire shaped like a spring. It was first developed and trademarked by STANLEY Engineered Fastening and is now widely used across many industries.
The insert is installed into a hole that has been drilled and tapped to a specific size. Once installed, it creates a brand-new internal thread that matches the original bolt or screw. When the bolt is tightened, the helicoil insert expands slightly and grips the surrounding material.
This action spreads the load evenly instead of stressing one weak spot. It helps prevent future thread damage and ensures the joint remains secure under load.
Why Helicoil Inserts Are Used to Fix Stripped Threads
Threads usually strip because of over-tightening, vibration, repeated use, or working with soft materials like aluminum or plastic. Simply re-tapping the hole removes more material and often makes the problem worse. Replacing the entire part can also be slow and expensive.
A helicoil insert fixes the problem by reinforcing the hole instead of weakening it. It brings the thread back to its original size, which allows you to keep using standard bolts. This greatly extends the life of the part.
For many repair and maintenance teams, helicoil inserts are the fastest and most cost-effective solution. They provide a high-strength connection without requiring significant design changes.
Are Helicoil Inserts Stronger Than Original Threads?
Helicoil inserts are often stronger than original threads because they are made from high-strength stainless steel. This is especially true in soft materials like aluminum, magnesium, or plastic.
Since the insert is stainless steel, it handles wear and corrosion better than the base material. The load is spread across the entire insert instead of being concentrated in one area. This makes them a good choice for parts exposed to vibration or frequent removal.
The stainless steel material also prevents “galling” or seizing of the fastener. This ensures that maintenance can be performed multiple times without damaging the threads again.
Where Helicoil Inserts Are Commonly Used
Helicoil inserts are used in industries where threaded holes are under high stress or require frequent servicing. In automotive repair, they are commonly used to fix spark plug threads, engine blocks, and mounting points.
In aerospace applications, they help maintain strength while keeping parts lightweight. They are also used in electrical housings, industrial machinery, and rail systems. Any place where threads need to stay reliable over time is a good candidate for a helicoil insert.
Defense equipment and general manufacturing also rely on these inserts for long-term reliability. They allow for secure fastening in lightweight alloys that would otherwise fail under heavy torque.
How to Install a Helicoil Insert (Step by Step)
Installing a helicoil insert is simple when you follow the correct steps and use the right tools. Most helicoil kits come with everything you need, including the correct drill bit, tap, and installation tool.
Drill Out the Damaged Threads
Start by drilling out the stripped or damaged threads using the drill size recommended in the helicoil kit. Make sure the drill is straight to avoid misalignment. If you’re working with aluminum or harder metals, use cutting fluid to reduce heat and prevent the drill bit from clogging.
Tap the Hole to Create New Threads
Next, use the special tap included in the kit to cut new threads in the drilled hole. Turn the tap slowly and apply cutting fluid to keep the threads clean and smooth. Once the threads are fully cut, carefully reverse the tap to remove it from the hole.
Install the Helicoil Insert
Place the helicoil insert onto the installation tool and thread it into the newly tapped hole. Turn the tool clockwise until the insert sits about a quarter to half a turn below the surface. Do not over-tighten. Once the insert is seated, remove the installation tool.
Common Helicoil Insert Mistakes to Avoid
Using the wrong drill size is one of the most frequent causes of helicoil insert failure. If the hole is drilled too large, the insert won’t grip the surrounding material properly and may spin or pull out under load. Always use the exact drill size specified in the kit.
Misalignment during drilling or tapping is another common problem. If the drill or tap is not kept straight, the threads inside the hole will be angled. This causes the helicoil insert to sit crooked, which makes the bolt difficult to install.
Installing the insert too deep or leaving it flush with the surface can also create issues. A helicoil insert should sit slightly below the surface so the bolt can fully seat and clamp properly. Finally, always clean the hole thoroughly to remove metal chips or debris before installation.
Helicoil Insert vs Other Thread Repair Options
Helicoil inserts offer a high-performance alternative to standard re-tapping or using solid threaded inserts. While solid inserts can handle higher loads, they require more material removal.
Thread Repair Comparison Table
| Repair Method | Material Removal | Strength Benefit | Space Required |
|---|---|---|---|
| Helicoil Insert | Low | High | Minimal |
| Solid Insert | High | Very High | Significant |
| Re-tapping | Moderate | Low | Minimal |
Compared to re-tapping a hole, a helicoil insert offers better strength and longer service life. Solid threaded inserts can handle higher loads in some cases, but they require more material removal and more installation effort. Helicoil inserts are often the better choice when space is limited or weight matters.
Restoring Industrial Joint Integrity
A helicoil insert is a reliable way to fix damaged threads and extend the life of parts that would otherwise need replacement. When installed correctly, it restores the original thread size and improves strength in softer materials. This helps prevent future failures caused by vibration or repeated use.
The efficiency of this repair method makes it a staple in professional manufacturing and maintenance environments. It allows teams to return equipment to service quickly without compromising on safety or performance standards. By reinforcing the base material with stainless steel, the joint often becomes more durable than the original design.
Whether you’re working in automotive repair, aerospace maintenance, or general assembly, helicoil inserts offer a proven way to keep equipment running longer. They represent a technical solution that balances cost, speed, and mechanical performance. Maintaining a supply of these inserts ensures that thread damage never becomes a permanent bottleneck in your production or repair workflow.
Frequently Asked Questions (FAQs)
What is a helicoil insert used for?
A helicoil insert is used to repair stripped or damaged threads in a hole or to provide stronger threads in soft materials like aluminum. It allows you to restore a hole to its original size so you can keep using the same bolts.
Do I need a special tap for a helicoil?
Yes, you must use a specific “STI” (Screw Thread Insert) tap that matches the helicoil size. A standard tap will not work because the hole needs to be slightly larger to accommodate the thickness of the wire insert.
Can a helicoil insert be removed?
Yes, a helicoil insert can be removed by using a small tool to grab the top coil and pull it out. However, removing it usually destroys the insert, so you will need to install a new one to restore the threads.
Are helicoil inserts permanent?
Yes, helicoil inserts are considered a permanent repair when installed correctly. Once the insert is seated in the tapped hole, it stays in place due to the outward spring pressure and shouldn’t move during normal use.
Why did my helicoil insert fail?
The most common reasons for failure are using the wrong drill size, failing to tap the hole correctly, or improper cleaning of the hole. If the hole is too big, the insert can’t grip the material and will pull out.
Can helicoil inserts handle high heat?
Yes, because they are usually made from stainless steel, helicoil inserts can handle high temperatures. This makes them ideal for engine repairs, such as fixing spark plug holes or exhaust manifold bolts.
