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How do I repair a damaged thread in 4 steps?

December 20, 2017

There are various causes that can lead to the destruction of threads, for instance corrosion, wear or a too high tightening torque. In this article we will explain how to fix the damaged thread.

Before you can start repairing the damaged thread, you will need the following tools:

  • drilling machine
  • twist drill
  • single-cut tap
  • tap wrench
  • fitting-tool
  • thread insert
  • pin-breaker
  • (cutting oil, when available)

Make sure in advance that the single-cut tap and thread insert match and have the right size and same pitch.

In our example, the thread is free, so there is no broken screw. We describe how to remove such a broken screw in our article "How to remove a broken screw from a workpiece?".

The thread repair

Pin-breaker

Drill thread

First you drill the damaged thread with a twist drill. The twist drill must match the size of the thread diameter.

You can find an overview of the required diameter (core holes) in this table (PDF).

In the case of a new metric thread with e.g. M 8 you need a twist drill with a core hole of 6.8 mm.


Single-cut tap

Cut thread

Now you can cut the new thread with the single-cut tap. To do this, place the single-cut tap in the tap wrench and cut by hand into the drilled hole (see first picture below).

If you have cutting oil on hand, you can use it well here.

This new thread is used in the next step to accommodate the thread insert.


Thread insert

Insert thread insert

Put the thread insert on the fitting-tool or directly into the hole (see second picture below). The pin (the transverse part in the middle of the thread insert) must sit down in the groove opening.

Turn the thread insert under slight pressure in the thread direction (see third picture below).

Attention: DO NOT turn against the direction of rotation otherwise the pin could break off.


Pin-breaker

Break pin

Crack the pin of the thread insert with the pin-breaker at the bottom of the thread.

You are all done: The new thread is now ready for use.

Thread repair tools

We have a thread repair set in our range of products. So you have all the tools you need to easily and quickly make repairs to damaged and worn threads.

You can find all products for thread repair under https://www.ruko.de/en/products/thread-repair-tools.

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