How to repair damaged thread

Written by thomas west
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If you do many repairs on your home or car, you have probably encountered a nut, bolt or other fastener with stripped or damaged threads. Threads allow two fasteners to be twisted together and, when tight, will hold many times their own weight. A thread may be damaged by cross-threading, which is when the fastener is twisted onto its receiving end at an angle, causing the threads on each part to cross each other instead of gliding together as designed. Threads might also be damaged when parts are rusted together and are forced apart when removal is necessary. With the right tools, damaged threads can be repaired to work as new again.

Skill level:

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Things you need

  • Tap and die set
  • Thread gauge
  • Die wrench
  • Tap wrench
  • Cutting oil
  • Vice

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    How to Repair Male Threads

  1. 1

    Use a die if your damaged fastener has male threads, such as a bolt. Hold a thread gauge to the threads on the bolt or fastener to determine the correct size of die to use.

  2. 2

    Place the bolt in a vice with the damaged threads facing upwards so you will have better control of the die.

  3. 3

    Apply a small amount of cutting oil on the damaged threads of the bolt so that the die will turn more easily.

  4. 4

    Place the correct size of die into a die wrench and tighten the thumb screw in a clockwise direction. Place the die over the end of the bolt. Began turning the die in a clockwise direction for about one half turn and then stop. Use a back and forth motion to break up the chips of metal that have been cut by the die. Continue this step until all of the damaged threads have been recut by the die.

  5. 5

    Turn the die wrench in a counterclockwise direction to remove it from the threads. Remove the bolt from the vice.

    How to Repair Female Threads

  1. 1

    Use a tap to repair the female threads of a fastener, such as a nut. Place the fastener in a vice.

  2. 2

    Use a thread gauge on the threads to find the correct size of tap to use. Clamp the tap wrench to the tap and tighten the thumb screw in a clockwise direction.

  3. 3

    Apply cutting oil to the damaged thread to lubricate the tap when cutting.

  4. 4

    Place the tap into the threads and turn the wrench handles in a clockwise direction for half a turn. Work the tap in a back and forth motion to break up the chips of cut metal. Repeat this step until the tap has been run completely through the fastener.

  5. 5

    Remove the tap from the fastener by backing it out in a counterclockwise direction. Remove the fastener from the vice.

Tips and warnings

  • You can turn a tap or a die with an adjustable wrench, but you will make a straighter cut and have less of a chance of breaking your tap or die by using a die wrench or a tap wrench. The tap or die fits into the wrench and has handles on either side, as opposed to an adjustable wrench with only one handle.

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