Valve core thread dimensions

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

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

On Fri, 22 Sep 2006 22:39:11 -0600, wrote:

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.

Shraeder external - 0.305-32 (5/16-32 UNEF will do)
Schraeder internal - 0.206-36 (#12-36 is a bit big)
Presta main - m6-0.75
Presta cap - m5-1.0

wrote:
On Fri, 22 Sep 2006 22:39:11 -0600, wrote:

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.

Shraeder external - 0.305-32 (5/16-32 UNEF will do)
Schraeder internal - 0.206-36 (#12-36 is a bit big)
Presta main - m6-0.75
Presta cap - m5-1.0

The other approach is to thread the stub internally and use a removable
presta valve used on some brands of tubulars and at least some
Continental inner tubes.

I have no clue as to the thread for this.

Marcus

On Sat, 23 Sep 2006 10:51:51 GMT, wrote:

Presta main - m6-0.75
Presta cap - m5-1.0

Both of those are remarkably uncommon sizes. Good luck finding a tap
or die in those thread and diameter combinations outside of a
specialty tool supplier.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Mon, 25 Sep 2006 17:58:54 GMT, Werehatrack
wrote:

On Sat, 23 Sep 2006 10:51:51 GMT, wrote:

Presta main - m6-0.75
Presta cap - m5-1.0

Both of those are remarkably uncommon sizes. Good luck finding a tap
or die in those thread and diameter combinations outside of a
specialty tool supplier.

Got both of 'em in a cheap carbon-steel set at the local discount tool
emporium. You must live in a tool-parched land.

On Mon, 25 Sep 2006 18:05:51 GMT, wrote:

On Mon, 25 Sep 2006 17:58:54 GMT, Werehatrack
wrote:

On Sat, 23 Sep 2006 10:51:51 GMT, wrote:

Presta main - m6-0.75
Presta cap - m5-1.0

Both of those are remarkably uncommon sizes. Good luck finding a tap
or die in those thread and diameter combinations outside of a
specialty tool supplier.

Got both of 'em in a cheap carbon-steel set at the local discount tool
emporium. You must live in a tool-parched land.

Dear J & W,

Hmmm . . . I'd split the difference between your positions.

Lots of cheap tap and die sets in the U.S. include m6 x 0.75, but none
seem to include m5 x 1.0.

Here's an $8 Harbor Freight set with m6 x 0.75, probably good enough
for the metal in valve stems:

http://www.harborfreight.com/cpi/cta...emnumber=39384

Sears doesn't even bother to list details in their tap and die sets
beyond "60 pieces" and seems to have nothing as m5 x 1.0.

This place offers a 5 mm x 1.00 die for $8.50:

http://www.victornet.com/cgi-bin/vic...,90 5,606,607

Cheers,

Carl Fogel

In article ,
Werehatrack wrote:
On Sat, 23 Sep 2006 10:51:51 GMT, wrote:

Presta main - m6-0.75
Presta cap - m5-1.0

Both of those are remarkably uncommon sizes. Good luck finding a tap
or die in those thread and diameter combinations outside of a
specialty tool supplier.

I don't believe these threads are correct. The presta valves
I've measured have inch-based thread pitches - 32 and 24 tpi
respectively.
But in this case, I think the OP was looking for neither of
these, but rather the internal thread in a removable-core valve stem.
That, I haven't measured.

However, I think it's a moot point: there's more going on inside
the valve stem than just that thread - the seating area that the valve
core seals against needs to be shaped appropriately too, and it seems
like more trouble than its worth to try to reproduce it all.

Were it me, I'd probably just slather some epoxy in the stem
where the crack is, and permanently glue an extension in place, letting
the epoxy seal whatever crack is there.

-Luns

On Tue, 26 Sep 2006 00:31:05 +0000 (UTC),
(Luns Tee) wrote:

In article ,
Werehatrack wrote:
On Sat, 23 Sep 2006 10:51:51 GMT, wrote:

Presta main - m6-0.75
Presta cap - m5-1.0

Both of those are remarkably uncommon sizes. Good luck finding a tap
or die in those thread and diameter combinations outside of a
specialty tool supplier.

I don't believe these threads are correct. The presta valves
I've measured have inch-based thread pitches - 32 and 24 tpi
respectively.
But in this case, I think the OP was looking for neither of
these, but rather the internal thread in a removable-core valve stem.
That, I haven't measured.

However, I think it's a moot point: there's more going on inside
the valve stem than just that thread - the seating area that the valve
core seals against needs to be shaped appropriately too, and it seems
like more trouble than its worth to try to reproduce it all.

Were it me, I'd probably just slather some epoxy in the stem
where the crack is, and permanently glue an extension in place, letting
the epoxy seal whatever crack is there.

I rechecked the dimensions; 6x.75 and 5x1.0 are correct for Presta
externals on all of mine. 1.0 is very close to 24tpi, and .75 is
close to 32tpi, but the thread guage for the metrics was clearly a
better fit than the US guage. While mixed metric/inch thread choices
have been seen elsewhere on bikes (notably on some Raleigh bits as I
recall), the Presta stem apparently isn't one of them.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

In article ,
Luns Tee wrote:
Presta main - m6-0.75
Presta cap - m5-1.0

I don't believe these threads are correct. The presta valves
I've measured have inch-based thread pitches - 32 and 24 tpi
respectively.

I don't believe I should continue to trust my memory. I remember
being surprised with what the threads turned out to be, and it involving
inch pitches, but extrapolated that too far.

The main shaft threads are indeed metric, although it's a 0.8mm
pitch rather than 0.75.

My surprise was with the cap threads, which on looking at them
again, still seem to be 24tpi to me. With only three thread crests at
most, it's very hard to discern a difference between 24tpi and 25.4tpi,
but this just highlights how unimportant the matter is.

Trying to determine the gauge by looking at thread crests is
misleading, as the final turns are truncated, making the apparant crests
closer spaced than the actual pitch.
Comparing against a 1.0mm reference, the crests appear to match,
and the threads seem to fit, but on the valves I checked, contact is
on the flanks of the outermost turns of thread, with the middle turn
making no contact at all, and crests not reaching the thread root.
The orientation of the contact indicates the thread is a coarser
pitch than 1.0mm.
Putting a 24tpi gauge against the cap threads, the gauge's
crests land consistently in the valve's thread roots.

-Luns