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Old 03-10-2016, 03:10 AM   #1
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Join Date: Mar 2007
Location: Southwest Ohio
Posts: 2,939
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SUSP: Large Threaded Hole, Fix Damaged Threads, DIY Tap

If you've ever boogered up (technical term for damaged) the threads on a large threaded hole and had trouble finding a single tap to clean up the threads and you didn't want to buy a complete set of taps and dies just to get that one, here is a quick tip.

In my case, the top thread in one of the lower control arm holes for the radius rod bolts was damaged enough that I couldn't get a bolt to start. I didn't want to change out the control arm. Two hardware stores didn't have a 12 mm fine thread tap and I would have had to buy a large set at Auto Zone just to get the tap I needed. I didn't think about Harbor Freight until after they had closed. (Edit: Checked HF web site, only 12 mm 1.5 tap I could find was in an $85 set.) I normally don't pass up the opportunity to buy more tools, but I didn't want to wind up with a bunch of duplicates and I didn't figure I would need this size very often like some of the smaller sizes.

Tools needed:
Angle grinder with cutoff wheel (a hack saw may leave more burrs on the edges of the threads)
Sand paper (I used a belt sander)
Extra bolt of the desired size

If you have an extra bolt, cut a few (I cut four approximately 90 degrees apart) axial slots a few threads deep on the end of the bolt, then gently taper the last two or three threads on the end of the bolt with the sandpaper creating a psuedo tap. I was able to get this started in the hole and run it in without much effort to clean up the threads enough to where a normal bolt would easily engage.

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Last edited by fleetw00d; 08-01-2017 at 08:53 PM. Reason: additional information
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