Some of the threads that Campi (and I assume other Italian makers) used were based on the fact that England was the world leader in making most everything including nuts and bolts. I have no idea where "Italian" thread standards started, but it seems at some point both the pitch, i.e. 26tpi, and the thread form of 55 deg as used in Whitworth were taken up. But they decided to use metric for the O.D. Kind of weird but what the heck. French were very pure and non-engish with their own system using mostly that is now obsolete. When the Japanese came into the world market after the 1971 bike boom they decided to use English threads, kind of. JIS, a national standard bureau in Japan that makes standards for all products, made a book that describes most of the threads used on bicycles and parts made in Japan. Most of the threads are metric, but the BB and freewheel threads are English except the thread form is 60 deg not 55 deg as true English standard. This JIS standard thread system is now mostly the standard, although Italian BB is still used. JIS and Campi English is close but not quite the same. As mentioned on this thread the difference between 26tpi and 1.0 pitch is not much. At one point in my career I designed various bicycle parts that needed to mate with bikes that were made to mate with Campi parts. In order to come up with thread specifications for the manufacturers I did an analysis of threads on Campi BB, head sets, freewheel threads. I found that the variation was quite large, it made no difference for instance to use a hub market Eng. or It., the variation was larger than the theoretical size difference. I guess your question is what do you need to know to deal with all this? I would not worry at all about using a cutting tap M10x1 to clean out a rear hanger. All the other relevant threads are just normal metric sizes. The mention of thread rolling tap is not something to worry about. This is a tap without flutes, it forces the metal into a thread form. It is widely used on CNC machining, mostly because it leave not chips and will not break as easily on withdrawal. It is not normally used as a hand tap. If you have any other questions let's hear it.
Jim Merz Back in Big Sur CA
On Sun, Jul 18, 2010 at 5:04 PM, Jon Spangler <jonswriter@att.net> wrote:
> Dear Bob and all,
>
> Not being a machinist, and being easily confused by "hybrid" (Metric + SAE
> specs) sizing on threadings like 10MM x 26 TPI, I am lost when Bob mentions
> a
> "full roll" tap. A brief Google search gave me some not-quite-applicable
> machinist references, plus listings for Spinal Tap (definitely OFF-topic)
> and other distractions.
>
> Are there any good basic (simple enough for a home bike mechanic to
> comprehend) references about taps and threadings (mostly Metric in my case)
> that would not go too far into the "weeds" of production machining, CNC,
> etc.?
>
> For example, is there an all-metric sizing equivalent of 10 MM x 26 TPI?
>
>
> Thanks,
>
> Jon Spangler
>
> sleep-deprived as all get-out but enjoying the Tour de France none the less
> every morning at 5ish for the duration in
> Alameda, CA USA
>
> Jon Spangler
> Writer/editor
> Linda Hudson Writing
> TEL 510-864-2144
> CEL 510-846-5356
> JonSwriter@att.net
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>
>
>
> Message: 1
> Date: Sat, 17 Jul 2010 12:08:21 -0700
> From: Bob Freitas <freitas1@pacbell.net>
> Subject: Re: [CR] Derailleur hanger threads
> To: CLASSIC RENDEZVOUS <classicrendezvous@bikelist.org>
> Message-ID: <4C41FFA5.4080707@pacbell.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> The size is 10mm x 26tpi but a 10 x 1.0 tap is close enough
> (25.4) I recall the official Tap (Campagnolo?) was $25 back in the day
> but you could find a 10mm spark plug tap at most any hardware store etc
> for just a couple bucks and that will work fine.
> Downside of any 'thread cutting' tap is just that it cuts
> the thread so in multiple use situations you will end up with less that
> was there before.
> Notching a tool or even a 10 x 1.0 bolt might be better but best
> would be a 'full roll ' tap which reshapes and does not remove any
> material. This would be for damaged threads if you were converting an
> non threaded dropout a thread cutting tap would be required.
> I have seen thread files with a threaded end to repair
> inside threads but have never seen anything adjustable like we see for
> outside threads.
> Anyone who has knowledge of such an item I would like to see it
>
> BOB FREITAS
> Sunny MILL VALLEY, CA USA