How easily repair damaged threads with Helicoils

Introduction

Helicoils are a type of insert used to repair or reinforce damaged threads in metal parts.

They are available on the market under different names depending on the manufacturer (Helicoil , V-coil, Elicel , ours Spiralock ) and comply with DIN 8140.

Helicoil wire thread inserts provide a permanent and reliable solution for torn, damaged or worn threads.

A thread insert Helicoil resembles a spiral spring and fits into a specially tapped hole, creating a new thread. Helicoils, in fact, allow the original thread size to be restored, perfectly compliant and even more robust than original one.

Helicoil kits are useful in automotive and machinery repairs when threads are damaged by overuse, corrosion or other problems.

They represent a convenient repair solution, both in terms of time and costs. With the right tools, Helicoils can be installed quickly and thus allow to avoid the replacement of more expensive parts

When to Use Helicoils

Common examples where helicoils can be used:

• Engine bolt holes that have been stripped or corroded;

• Holes in machinery and equipment with worn threads;

• Holes in automotive parts such as cylinder heads, transmission housings, or intake manifolds;

• Holes in firearm components, such as receivers and barrels that have damaged threads;

• Thread reinforcement on components made of light and fragile alloys, such as aluminium and cast iron in the military, naval, aerospace and railway sectors

Helicoil Insert Sizes

Helicoil inserts come in a wide variety of standard sizes to repair both metric and inch sized threaded holes.

The thread is characterized by three dimensions: diameter, pitch and length. The latter is expressed in reference to the diameter or in millimetres. For example M 6 x 100 x 1.5D identifies a thread for an M6 screw with pitch 1 and length 9 mm (1.5 times the diameter).

Some of the most common sizes include:

• for metric threads the standard helicoil insert sizes are: M3, M4, M5, M6, M8, M10, M12;

• for threads in pollici: 4-40, 6-32, 8-32, 10-24, 10-32, 1/4"-20, 1/4"-28, 5/16"-18, 5/ 16"-24, 3/8"-16, 3/8"-24, corresponding to common UNC and UNF bolt sizes.

Larger sizes are also available (M14, M16, M18 and beyond, up to very large sizes such as M45), but also smaller sizes for precision applications (down to M2).

The size directly corresponds to the original thread to be repaired. So M8 x 1.25 helicoil is designed for an M8 hole, while a 1/4"- 20 insert will match 1/4"- 20 threaded holes.

To identify the correct size of Helicoil to use, you must refer exclusively to the screw to be inserted and choose the thread of the same diameter and pitch and appropriate length related to the screwing depth.

Refer to the Helicoil table which also indicates hole sizes to prepare for correct tapping.

Click here to view Helicoil Table

Helicoil Insert Materials

Helicoils are available in a wide range of materials to suit different applications and conditions such as operating temperature, corrosion resistance requirements, weight considerations and other special requirements.

Most common Helicoil materials are:

• Stainless steel - Is a popular choice for Helicoils due to its strength, corrosion resistance and relatively low cost. The manufacturing standard is AISI 304, X5CrNi18-10 stainless steel

  
  

• AISI 316 stainless steel - For marine applications, AISI 316 stainless steel threads, X6CrNiMoTi17-12-2, are available

  
  

• Bronze - bronze wire thread inserts provide good corrosion resistance and do not produce sparks, making them particularly suitable for electrical threads or threads made in hazardous locations. On the other hand, bronze is softer and less resistant than steel

  
  

• Inconel - It is a nickel-chromium alloy that offers excellent resistance to temperatures up to 750° and good resistance to corrosion

Helicoil Types

In addition to the standard wire thread threads, used for common applications, there are some specific variants:

• Screw-locking helicoils - thanks to the polygonal shaped spiral, these wire thread inserts exert a braking action on the screw, making them particularly suitable for applications subject to vibration

  
  

• Tangless helicoils - These thread inserts are characterized by the absence of a drag tang. Since the tang does not require removal after insertion, they allow for a faster installation process, especially when large quantities need to be inserted. However, they entail a higher cost for both the installation tools and the threads themselves

Helicoil Kits

Helicoil thread repair kits contain all the tools and parts needed to repair a stripped or damaged thread using helicoil inserts.

A typical single-size Helicoil Kit includes:

• Helicoil Tap - is used to prepare threads in the hole where helicoil insert is going to be installed. Helicoil inserts in the kit match the tap diameter and thread pitch

  
  

• Helicoil Installation Tool - is used to insert the helicoil into the prepared hole. It has a mandrel that grips the insert and guides it into the threads in the hole

  
  

• Drill Bit - Some Helicoil kits include also a drill bit, the use of which reduces wear on the tap and makes cutting new threads easier

There are also multi-size Helicoil Kits available, containing most popular diameter e pitch combinations

To consult the Helicoil Kit Catalog click here

How to install Helicoils

1. Prepare and clean the damaged thread using the drill bit of the size suggested in the table (see Helicoil Table)

   
   

2. Tap the new oversized thread with the appropriate helicoil tap, making sure to work precisely. Correct tapping is essential for a perfect assembly

   
   

3. Select the Helicoil of the correct size by ensuring the outside diameter matches the hole size

   
   

4. Place the threaded insert onto the thread inserts installation tool and rotate it through the pre-winder nose and then into the thread prepared in step 2

   
   

5. Keeping the installation tool in line, slowly rotate the Helicoil into the hole without applying pressure

   
   

6. Continue threading the helicoil inside the hole until you reach the desired depth

   
   

7. If there is a through hole, remove the drive tang with the appropriate cutting tool

How to remove a Helicoil

If necessary, a Helicoil insert can be uninstalled easily with a thread insert extractor. Place this tool on the thread and tap the rod lightly. This will grip the insert inside the thread insert and allow it to be removed with a counterclockwise rotation

Advantages of Helicoils 

• Restore the thread to its original size

• Helicoil wire thread inserts are strong and durable. They provide a permanent and reliable repair solution

• Quick and easy installation. With a little practice, Helicoils can be installed without complications with basic tools

• Available in a wide range of sizes. Thread inserts are available in metric and SAE sizes to accommodate most common screw sizes

Overall, Helicoils are the ideal option for repairing most common damaged threads in metal parts. When used correctly, they create strong and durable threads, even better than the original

Other solutions to restore threads

In specific contexts, such as field repairs, high-stress environments, soft materials, or when dealing with dented or rusted threads, Helicoils may not be the best solution when repairing damaged threads.

Ensat self-tapping inserts, Keenserts or NES tools are valid alternatives to Helicoils in these situations.

• Ensat self-tapping inserts - Ensat inserts are cylindrical self-tapping inserts with cutting edges on the external surface that allow them to be screwed directly into the material without pre-threading. Compared to Helicoils, Ensats are often preferred when greater tensile strength and a more stable hold are required, especially in low-hardness materials

  
  

• Keenserts - Keensert inserts are threaded inserts with locking keys, which are inserted at the end of the installation to ensure extreme security against loosening. They are often used in high stress applications and in critical environments, such as in the aerospace or automotive industries, where it is necessary to prevent any risk of thread pullout

  
  

• Nes thread repair tool - Nes are, instead, an excellent solution when the thread is only slightly damaged, rusted or oxidized. These are universal tools that allow you to recover the existing thread without the need for an insert or a new hole. To find out more about Nes, read the article

Consult here the complete Catalogue and the Technical Data Sheets of the products that you find available online. All popular sizes both metric and inch are in stock