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Old September 23rd 06, 05:39 AM posted to rec.bicycles.tech
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Default Valve core thread dimensions

On Thu, 21 Sep 2006 15:31:46 GMT, "Mike Kennedy"
wrote:

Does anyone know what the thread dimensions are for a value core or the
threaded end of a valve extender? I have a split in the valve stem of a TUFO
tubular-clincher and I thought that I would cut the section off that has the
split, tap the section left and install an valve extender. Anyway I need to
know what threading to tap.

Thank you,

Mike Kennedy


Dear Mike,

There are actually two threads on a typical Presta valve stem.

One is the long base, which is wide and threaded for the jam nut that
is tightened down to the rim. "Smooth" Presta valves lack this
threading.

The other threaded section at the end of the valve. It's narrower than
the main body of the valve stem, has only about 3 threads, and is for
the valve cap (or a typical valve extender).

So your scheme may not work too easily, even if you know the thread
pitch and find a die. It sounds as if you want to cut off the end of
the valve stem with the crack, including the short, narrow part that
the valve cap or typical extender just barely threads onto.

If so, you'll have an uncracked stub left, but it will be too thick
for a typical valve extender and will have to be turned down somehow
before threading.

In any case, I'm damned if I can find either thread pitch on the
internet, even in the U.S. Patent Office site. I've emailed a company
that makes extenders and asked if they'll reveal the secret dimension.
A real mechanic would simply measure the threads with a gauge, but
I've seen enough loosely-fitting extenders to wonder just how easy the
measuring of such small threads is. Most of the extenders that I've
seen worked much better with a couple of twists of teflon plumber's
tape around the threads to seal the connection.

You'd also have to cut the very end off a Presta valve to get the
little knurled nut off, slip the valve through the extender, and put
the screw back on.

A new Tufo clincher-tubular is probably a lot less fuss.

Cheers,

Carl Fogel
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