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Repair Damaged Nuts and Bolts

A rethreading kit is an important part of any automotive toolbox. Use it to restore stripped threads on old, rusty nuts and bolts when you don't have time to search the stores for a replacement.

By the DIY experts of The Family Handyman Magazine

Start by finding the thread count

No matter how careful you are when you reinstall old rusty nuts and bolts, someday you're going to strip some threads. Of course it will happen on a critical bolt, on a Sunday night when all the stores are closed. That's when a thread restoration kit pays for itself. A full set (metric and SAE) will quickly put irreplaceable and hard-to-find nuts and bolts back into service. The rethreading tools look like traditional taps and dies. But instead of cutting new threads, they reshape them to original condition.

To restore bolt threads, start by finding the thread count (SAE) or pitch (metric). Hold the thread file against the bolt threads until you find the size that matches. Clamp the bolt in a vise, engage the thread file grooves with the bolt threads and push the file (Photo 1). That “resets” the threads enough so you can screw on a rethreading die (apply a few drops of oil first). Use a rethreading tap to restore threads on nuts or threaded engine component holes. Don't try to rethread the entire bolt, hole or nut in one operation. Insert the rethreading tap or die and rotate a few turns, then back it off a full turn. That will dislodge the debris from the teeth.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Rags
    • Vise
    • Wrench set

You'll need a thread restoration kit from an auto parts store.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • Lubricating oil

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February 04, 9:10 PM [GMT -5]

Good article. I've used my sets countless times over the years. My first thread file belonged to my grandfather and now is probably over 70 years old and still works perfectly. I finally purchased a metric version several years ago as metric fasteners became more prevelent. During my years as a service technician I also had purchased both the thread taps and dies. One addtional item a person may want to add is an actual thread file. These are designed with a hardened tapered file edge to be used in the bolt pitch. Great for starting the clean-up process on the end of a bolt before using a rethreading die. Another tip for using a rethreading die is to install it on a bolt thread before cutting off a length of the thread. You then can remove the die giving you relatively clean threads at the end of a bolt.

Reminder about using rethreading taps and dies; while they are hardened steel, they are designed to cut new internal or external threads. Attempting to do so will damage or break the rethreading die. Always use threading taps and dies for cutting new threads.

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