Start by finding the thread count
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Photo 1: File threads
Reset the threads with a thread file before screwing on the rethreading die.
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Photo 2: Rethreading kit
Rethreading kits are available at auto parts stores and online. Buy a full set for both metric and SAE nuts and bolts.
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Photo 3: Tap
Use a rethreading
tap on nuts and threaded holes.
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Photo 4: Rethreading die
Clean rusty or stripped threads with a
thread restoration die.
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.