M10 x 1 vs M10 x 26

Jimbolina · Sep 24, 2009

Guys, I'm wanting to mount an older Campy NR rear derailleur onto a new (aluminum) De Bernardi Zonal frame, but the derailler hanger is 10mm x 1 threading, rather than the 10mm x 26 found on the Campy hanger bolt.

My question is, can I simply take a NR derailleur bolt and slowly work it in with oil, and occasionally backing it out to clear the threads, or is there a better method? I want to do this right.

Apparently it is impossible to get a 10mm x 26 tap to retap this hole.

Thanks for your help,
Jim

asad137 · Sep 24, 2009

You sure about those sizes? A 10mm screw with a 26mm pitch (distance between thread crowns) doesn't really make sense.

In general, though, you can't retap a hole that's been tapped for one thread pitch into another, even (actually...especially) if it is the same major diameter (10mm in this case).

Asad

Jimbolina · Sep 24, 2009

Yes - the bolt is a 10mm fastener with a 26 pitch.

The frame is supposedly a 10mm with a 1 pitch. Same size as an old Campy (rear) axle.

Jim

asad137 · Sep 24, 2009

Jimbolina said:
Yes - the bolt is a 10mm fastener with a 26 pitch.

The frame is supposedly a 10mm with a 1 pitch. Same size as an old Campy (rear) axle.

I think you might be getting pitch (distance between thread crowns) and threads per length mixed up. Thread pitch = 1/threads per length. Like I said, a 10mm bolt with 26mm between thread crowns doesn't really make sense, as it wouldn't work very well as a bolt. Is it 26 threads per cm? 26 threads per inch (which would actually be very close to a 1mm thread pitch)?

Asad

JCavilia · Sep 24, 2009

yeah

asad137 said:
I think you might be getting pitch (distance between thread crowns) and threads per length mixed up. Thread pitch = 1/threads per length. Like I said, a 10mm bolt with 26mm between thread crowns doesn't really make sense, as it wouldn't work very well as a bolt. Is it 26 threads per cm? 26 threads per inch (which would actually be very close to a 1mm thread pitch)?

Asad

It's 26 TPI, which as you finally conclude is "close" to 1 mm pitch. Threads per a given length is just another (reciprocal) way to express pitch.

The OP's question is whether it's close enough to re-tap it and have it function, and I don't know the answer to that.

Assuming that would work (and he assumes it would) his other question is whether he can use a bolt rather than an actual tap to accomplish that. I think that will work, especially with a steel bolt and an aluminum frame. You can modify a bolt into a crude tap with a little file work. file down the threads at the end a little so the diameter tapers a bit, and then file a little tapered wedge longitudinally from the end of the bolt. this will provide a little cutting face on each thread.

You only have 5 or 6 threads, so it might work even if it's not perfect. If the derailleur has a nut for the protruding end of the bolt you should be able to make it secure enough.

Oh, one more point. If you have an older Campy rear hub around, the threaded axle is the same thread as the hanger, and might make a good improvised tap. The threaded axles are pretty tough steel, I think.

Jimbolina · Sep 24, 2009

Thanks JC!

Yes TPI is what I was looking for. 10mm x 1tpi vs 10mm x 26tpi.

The tapering of the bolt thread idea sounds good, and I can Dremel in a couple of channels along the shaft to give the cut somewhere to go.

Thanks again,
Jim

Squidward · Sep 24, 2009

Jimbolina said:
Yes TPI is what I was looking for. 10mm x 1mm vs 10mm x 26tpi

Fixed it for you.

I think you should be able to just bolt that RD on without any issues. The thread pitch is close enough (1mm = 1/25.4 vs 26 TPI which is 1/26).

asad137 · Sep 24, 2009

Squidward said:
I think you should be able to just bolt that RD on without any issues. The thread pitch is close enough (1mm = 1/25.4 vs 26 TPI which is 1/26).

I would tend to agree if you only have about 5 threads to deal with. Over 5 threads the difference in thread crown position is only 0.0045", which will probably work fine. The act of threading in the bolt will likely slightly deform the threads a little anyway to force them to the correct spacing.

Asad

Kerry Irons · Sep 25, 2009

Rethinking

Jimbolina said:
Guys, I'm wanting to mount an older Campy NR rear derailleur onto a new (aluminum) De Bernardi Zonal frame, but the derailler hanger is 10mm x 1 threading, rather than the 10mm x 26 found on the Campy hanger bolt.

My question is, can I simply take a NR derailleur bolt and slowly work it in with oil, and occasionally backing it out to clear the threads, or is there a better method? I want to do this right.

For at least the past 40 years, there has only been one standard size for derailleur attachment bolts. You are getting worked up over typographical errors or translation problems. Campy NR will fit any current derailleur hanger. No question.

dave2pvd · Sep 25, 2009

Kerry Irons said:
For at least the past 40 years, there has only been one standard size for derailleur attachment bolts. You are getting worked up over typographical errors or translation problems. Campy NR will fit any current derailleur hanger. No question.

I agree.
Never seen metric fasteners described in TPI. Metric is always
MDiameterxPitch

FBinNY · Sep 25, 2009

dave2pvd said:
I agree.
Never seen metric fasteners described in TPI. Metric is always
MDiameterxPitch

The OP is correct in his info. For many years Campy used a 10mm dia. thread with a 26tpi pitch for the RD hanger. Axles were also 26tpi for many years, until both were phased out, axles first, than the RD hanger only in the last few years.

These hybrid threads were not unique throughout post war Europe, and were a direct result of the Marshall Plan, whereby USA built lathes and other machine tools were sent to help with wartime reconstruction. The screw cutting lathes generated thread pitch off a leadscrew using a mechanical gearbox, and since there is no way to generate a metric pitch off an inch leadscrew hybrid threads became popular in many applications. Campy's 10x26tpi hanger bolt may have been the last vestigial trace of this bit of history.

Meanwhile, to the OP, if you want I have 10x26 taps and can sell you one, or you can fudge the difference by using a cutting oil to prevent seizing while you work the bolt in and distort the thread as you propose. The error between is very slight totaling less than 1/6th of pitch over the 8 threads of engagement.

If it makes you more comfortable consider how many Shimano RDs were installed into Italian frame 10x26 hangers, or Campy RDs into non-Italian frames over the years.

dave2pvd · Sep 25, 2009

FBinNY said:
The OP is correct in his info. For many years Campy used a 10mm dia. thread with a 26tpi pitch for the RD hanger. Axles were also 26tpi for many years, until both were phased out, axles first, than the RD hanger only in the last few years.

These hybrid threads were not unique throughout post war Europe, and were a direct result of the Marshall Plan, whereby USA built lathes and other machine tools were sent to help with wartime reconstruction. The screw cutting lathes generated thread pitch off a leadscrew using a mechanical gearbox, and since there is no way to generate a metric pitch off an inch leadscrew hybrid threads became popular in many applications. Campy's 10x26tpi hanger bolt may have been the last vestigial trace of this bit of history.

Meanwhile, to the OP, if you want I have 10x26 taps and can sell you one, or you can fudge the difference by using a cutting oil to prevent seizing while you work the bolt in and distort the thread as you propose. The error between is very slight totaling less than 1/6th of pitch over the 8 threads of engagement.

If it makes you more comfortable consider how many Shimano RDs were installed into Italian frame 10x26 hangers, or Campy RDs into non-Italian frames over the years.

Wow. Good information there. Thanks!

To the OP: Suck it and see. If the derailleur bolt is too tight for comfort, and the cutting oil method doesn't work, run a taper M10x1 tap through there to clean up the threads some more.

DaveG · Sep 25, 2009

I must have been asleep that day in class!

FBinNY said:
The OP is correct in his info. For many years Campy used a 10mm dia. thread with a 26tpi pitch for the RD hanger. Axles were also 26tpi for many years, until both were phased out, axles first, than the RD hanger only in the last few years.

These hybrid threads were not unique throughout post war Europe, and were a direct result of the Marshall Plan, whereby USA built lathes and other machine tools were sent to help with wartime reconstruction. The screw cutting lathes generated thread pitch off a leadscrew using a mechanical gearbox, and since there is no way to generate a metric pitch off an inch leadscrew hybrid threads became popular in many applications. Campy's 10x26tpi hanger bolt may have been the last vestigial trace of this bit of history.

Meanwhile, to the OP, if you want I have 10x26 taps and can sell you one, or you can fudge the difference by using a cutting oil to prevent seizing while you work the bolt in and distort the thread as you propose. The error between is very slight totaling less than 1/6th of pitch over the 8 threads of engagement.

If it makes you more comfortable consider how many Shimano RDs were installed into Italian frame 10x26 hangers, or Campy RDs into non-Italian frames over the years.

Interesting piece of history; not sure where you picked that up from.

velo_artisanal · Jan 18, 2025

Very helpful thread and apparently the reference search result for questions involving threads on old Campa RDs. In case anyone is interested in my experience: Instead of forcing the 10mm x26TPI RD bolt into the 10x1 hanger, re-rapering the bolt with a 10x1 thread die works really well. The threads on the bolt become slightly thinner but the bolt then screws into the hanger without forcing and destroying the hanger threads.

M10 x 1 vs M10 x 26

Jimbolina

asad137

Jimbolina

asad137

JCavilia

Jimbolina

Squidward

asad137

Kerry Irons

dave2pvd

FBinNY

dave2pvd

DaveG

velo_artisanal

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