noscriptThread Repair | Cromwell Tools

Thread Repair

Choose Cromwell for a wide selection of thread repair kits and accessories online. Highly practical and easy to use, you can find a variety of thread sizes and kits to suit your requirements. We stock products from well-known, market-leading suppliers, like HeliCoil®, Kennedy-Pro® and Kennedy-ReCoil®.

What is thread repair?

A frequent problem when using tapped holes is that threads can become stripped or damaged. Once this happens you have two choices: either drill another hole or, where this isn't possible, repair the thread and re-establish a secure fit for the fastener. Thread repair involves widening and tapping the hole before fitting a helical thread insert so you can continue to use the same hole and the same fastener with minimal fuss.

When is thread repair used?

Used to repair or create a threaded hole to drive a fastener, thread repair kits and threaded inserts are a practical investment when fasteners are widely used or are made of softer materials.

Considerations when choosing thread repair

Hole diameter - Thread repair kits are available in single sizes such as M10, M12 etc or multiple sizes for the most flexibility.

Hole type - There are a wide variety of thread inserts available for each application, including through types, self-locking threads, tapered types and more to repair any tapped hole.

Insert length - A longer insert will provide greater tensile strength than a shorter thread insert. The material thickness must always be greater than the length of the insert, especially for through-hole types.

Thread material - The choice of insert materials offer different characteristics depending on the repair requirements. For example, carbon steel is the most common material and is suitable for most jobs, while stainless steel won't rust or oxidise and titanium delivers excellent strength for heavy-duty applications.

Thread repair jargon buster

We want to make it easy to choose the right insert for you. So, we've put together a brief definition of each type of thread insert...

• Free running inserts - the smooth wire coil is tangless and allows for the quick and simple repair of stripped threads in tapped holes.

• Locking inserts - these feature self-locking torque that secures fasteners against loosening due to impact or vibration.

• Strip feed insert reels - much like a reel of cable, this is a reel of fixed size helical inserts that can be snipped off when required. They are tangless due to the nature of their composition and are an economic solution to those who frequently repair threads.

• Tanged insert - a tang (part of the coil that sits centrally at the top of the insert) is designed for an insert tool to grip and turn the coil into place. For this type of insert a tang break-off tool is required and will be supplied in most thread repair kits.

• Tangless insert - These are ideal for through holes and can be inserted from either side and don't require tang break-off.


What's the strongest thread insert?

Titanium thread inserts deliver excellent strength and stability. They won't corrode and are suitable for use in most environments.

How deep should a threaded insert be fitted?

The hole for a threaded insert should be one and a half times deeper than the insert and should sit half a turn below the top of the hole.

Do I need glue to secure a threaded insert?

In some cases, yes glue will be specified by the manufacturer and in some cases supplied along with the insert. As an aside, another useful product when fitting an insert is cutting fluid, which helps to lubricate the tap when tapping the hole ready for the insert.