Introduction

How to re-thread a stripped or mis-threaded aluminum hole.

Tools

Parts

No parts required.

Determine which hole has the cross threaded or stripped screws.
  • Determine which hole has the cross threaded or stripped screws.

  • Determine the size of the current thread. Threads are called out by the outer diameter, a dash, and then the thread count. For example, the tap shown is 1/4"-20".

    • The hole's outer diameter can be determined by measuring the width of the screw or bolt that goes into the hole.

    • The thread count can be determined by counting the number of threads in one inch of screw length.

  • Select the appropriate tap size.

    • Taps are sharp. Do not handle the teeth.

  • Install the tap into the tap handle (See photo).

Some steps/ bullets have periods when others don't.

Iridian Vaca - Reply

Other than what I listed above, everything else looks good!

Iridian Vaca - Reply

Reword the bullet addressing the attire necessary to wear for the fix.

Iridian Vaca - Reply

Align the tap attached to the tap handle over the cross threaded or stripped hole.
  • Align the tap attached to the tap handle over the cross threaded or stripped hole.

  • For right hand screws, insert tap into tap hole as you slowly rotate the tap handle clockwise.

    • 99 percent of of holes, screws, and bolts are right hand screws. If you know your hole is a left hand thread, rotate counterclockwise instead of clockwise.

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Rotate the tap handle clockwise two full rotations, then counterclockwise 1/4 of a turn.
  • Rotate the tap handle clockwise two full rotations, then counterclockwise 1/4 of a turn.

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Repeat step three until you cannot easily rotate the the tap handle clockwise anymore.
  • Repeat step three until you cannot easily rotate the the tap handle clockwise anymore.

  • Rotate the tap handle counterclockwise until the tap is out of the part.

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Conclusion

After re-tapping your miss threaded check to make sure the threads work by screwing in the bolt or screw the hole is intended for

One other person completed this guide.

Kevin Tremaine

Member since: 04/09/2015

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1 Guide authored

Team

Cal Poly, Team 28-5, Green Spring 2015 Member of Cal Poly, Team 28-5, Green Spring 2015

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2 Comments

If the hole is truly stripped then the technique in this guide won't work because the hole would then be larger than it was originally and the tap won't bite into the metal and therefore not cut any new threads. So then there are two options:

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1. Choose the next larger size bolt and drill and re-tap the hole to fit that larger size. Or if you really must use the same size bolt then:

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2. Use a helical insert (aka "Helicoil") which is a coil of hardened steel wire that forms both a outer and inner thread.

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I used option #2 to fix a stripped hole in a bicycle shock absorber. I bought the Helicoil kit sized for my bolt from a automotive supply store. The kit came with the drill bit and tap sized for the outside threads of the coil. I drilled the hole, tapped the threads, then threaded the coil into the hole. The inside diameter of the coil was sized to fit the original bolt.

Don Barthel - Reply

Don is correct that tapping the hole as it exists won't really work and offered some viable solutions. However, if there isn't enough material for a Helicoil to bite into it won't work either on a through hole and sometimes using a larger bolt isn't an option either. In such cases you can add some filler to your existing hole. JB Weld can work as a filler for aluminum. If you apply a thin enough coating, you can tap the hole after it cures without drilling - then use a Helicoil for strength. Option 2 would be to use an aluminum filler rod and a MIG welder to fill, then drill and tap the hole.

ABCellars - Reply

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