On Wed, 27 Sep 2006 20:01:16 +0000 (UTC),
(Luns Tee) wrote:

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

Dear Luns,

Thanks--you and the others are making me feel better about not trying
to measure those tiny threads with my pathetic mechanical skills.

Here's what happened when I emailed a company and asked about the
threads on their Presta extender:

***

From:
To:
Sent: Friday, September 22, 2006 7:45 PM
Subject: Presta thread pitch and size?

Hello,

Can you tell me what the thread pitch and size is for the smaller
Presta valve cap section, the end part of the valve that your Presta
extender fits?

Thanks,

Carl Fogel

***

From: "Info @ Wheels Mfg"
To:
Subject: Presta thread pitch and size?
Date: Monday, September 25, 2006 6:57:58 AM

Not off the top of my head Carl. You could measure one!

Dave in sales

***

I note with alarm that the ubiquitous Daves who swarm on RBT are now
spreading even into the sales departments.

Cheers,

Carl Fogel