Fork Damper Rod Threads

johnod

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Oct 27, 2016
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Does anyone know what the threads at the top of the damper rods is?
I have to order a die.
Roadholders, featherbed.
Thanks
 
"Featherbed" should be 3/8 x 26 but apparently special (55 degree) Whitworth, not (60 degree) 26 tpi Cycle thread.
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"FORK DAMPER ROD (WHIT) (NM15801)(F11M/1049)"


The upper nut '14' is 3/8 x 26.
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I measured the dia. and it's 3/8, and I measured the thread with a thread gauge, and that read 26G.
I have no idea what the G is about, so that must be it i guess.

Thanks

Would that be what's called a BSW thread?
 
BSC. "C" is for "cycle thread", rather than fine, whitworth, pipe, etc.

To my knowledge, cycle thread is always 26 tpi.
 
johnod said:
I measured the dia. and it's 3/8, and I measured the thread with a thread gauge, and that read 26G.
I have no idea what the G is about, so that must be it i guess.

Thanks

Would that be what's called a BSW thread?
Click to expand...

It's special Whitworth or 'Whitform'.

According to AN, certain Norton threads are Whitform and not CEI/BSC. The damper rod according to AN is "WHIT" so not 26 TPI CEI/BSC as one would expect.
A 3/8" x 26 Whitform die isn't a common size (if it ever was?) and the only place I can find taps and dies is Tracy Tools...
www.tracytools.com

3/8" X 26 TPI W/FORM - Taps & Dies, Reamers, Milling Cutters, Tracy Tools

www.tracytools.com www.tracytools.com

...although 3/8" x 26 BSB (British Standard Brass) should be identical (or near-identical) as it's also a Whitworth thread.
www.tracytools.com

2" X 26 TPI W/FORM - Taps & Dies, Reamers, Milling Cutters, Tracy Tools

www.tracytools.com www.tracytools.com
 
Why in god's green earth would this thread be anything other than BSC 3/8x26 as described by everyone other than AN. The only place I know of where BSB threads are found on a Norton is Smiths instrument cables. As we all know,"Whitworth" is often used as a catchall for any British threads and I suspect even AN are guilty here.
 
t ingermanson said:
To my knowledge, cycle thread is always 26 tpi.
Click to expand...

Not always. Although various CEI pitches were not adopted into BSC (BS811) 20 TPI apparently was for a while but there's 40 TPI (1/8") and 32 TPI (5/32" & 3/16") also 24 and 30 TPI for "special applications".
 
The trouble with British bikes is ,obviously, not enough different, arcane, and obsolete thread forms used.
 
bearflag said:
I cannot find any other supplier who describes this as anything other than CEI/BSC, eg RGM.
Click to expand...

That's understandable as 3/8" x 26 would usually be BSC and I'd have said the same until Madnorton (of AN) said otherwise and as AN has factory drawings and other suppliers probably do not then I can't see them referring to a particular item as 'Whit' or 'Whitform' if it isn't.
 
This was new to me. Is there a particular reason for not using BSC threads in this application?

Does anyone know of a source for damper rods (06.7657) made of stainless steel? I would like to put an end to corrosion, which damages the damper tube caps as the rods move up and down.

-Knut
 
Last edited:
Peavey Jeltz said:
Looking at https://andover-norton.co.uk/en/shop-drawing/515/roadholder-front-forks

The nut that goes on the end of the dampener rod under the big top nut is 00.0003 which is a plain old 3/8" x 26 TPI nut and is used on other places on a slimline. If the thread on the dampener rod was that different wouldn't Norton have spec'd a special nut?
Click to expand...
Is that plain old 3/8" x 26 BSC or plain old 3/8" x 26 Whit Form as it doesn't say it is BSC, although there does seem to be a certain lack of consistency where one part is marked Whit or Whit Form and the other part is not.
 
000003 is a nut with CEI threads, made by AMC. At the opposite end, the thread appears to be 5/16"x26 CEI .... I bet the Whitworth thread info is a printing error.

-Knut
 
Last edited:
johnod said:
I measured the dia. and it's 3/8, and I measured the thread with a thread gauge, and that read 26G.
I have no idea what the G is about, so that must be it i guess.

Thanks

Would that be what's called a BSW thread?
Click to expand...
G is possibly for "gauge", ("Gage possible" alternative US spelling). My Whitworth set all has "G" after each tpi, while my UNF set doesn't.
 
It will be extremely difficult to distinguish 55 degrees and 60 degrees using a handheld gauge, as long as the pitch is the same. You will have to use a microscope to spot the difference.

The cited "Whitform" or "W/form" is informal language. You will not find this in a standard. Taps and dies sold by Tracey Tools go far beyond the standard, and are for special purposes. It's unlikely Norton/AMC used these.

Whitworth treads (as per standard BS 84) knows two entries for 3/8 bolts and nut only, it's the 3/8"x16 tpi BSW coarse, and the 3/8"x20 tpi BSW fine = BSF.

-Knut
 
ES234 said:
G is possibly for "gauge", ("Gage possible" alternative US spelling). My Whitworth set all has "G" after each tpi, while my UNF set doesn't.
Click to expand...
The 'G' on Whitworth pitch gauges as previously mentioned appears to refer to BSPP "external = G" pipe thread.
https://www.gewinde-normen.de/en/whitworth-pipe-thread.html

mdt-son said:
The cited "Whitform" or "W/form" is informal language. You will not find this in a standard. Taps and dies sold by Tracey Tools go far beyond the standard, and are for special purposes. It's unlikely Norton/AMC used these.
Click to expand...

Well, Ashley "Madnorton" of Andover Norton has said otherwise...
Madnorton said:
A few at most are 'Whit Form' we get most queries about these. You will not get them from a local fastener specialist. Why Norton used these is anyones guess.
Click to expand...
Madnorton said:
Yes, not all 20 & 26 tpi are Cycle, many assumed they were and bought Cycle threaded parts from other sources, only to query why they didn't quite seem right.
For what reason Norton decided to use 26 tpi Cei and Whit Form is still a guess, it seems to go against the BSA standards book.
Click to expand...
Madnorton said:
Whit form is used to describe a whitworth thread form used outside the normal table range of whitworth threads, usually with a different TPI. Or this may help others - a Whitworth thread you will find in a whitworth thread table, anything described as Whit Form you will not.
I have even had battles with fastener suppliers saying it can't be, only for their old and bold die makers to confirm it.
Click to expand...

...seems no reason to say that if there's no truth in it, also various pre-Unified AN items are marked 20 TPI Whit form. As there appears to have been no 20 TPI BSC series by this time then what thread form is it, if not Whit form?:

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Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
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Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk

I will PM Madnorton and ask if he can clear this up.
 
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