…..what thread form a 9/16 20tpi thread is? It's not BSF,UNF or CEI (It's on the crank mainshaft of a Velocette)

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If your dreams don't scare you, they are not big enough.

Sounds like British Standard Cycle. Tracey Tools will sell you taps and dies...

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08 Specialized Langster

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Buell Ulysses XB12X 06/08

Cycle thread was my first choice too, but it turns out to be 26tpi. UNF is the nearest at 18 tpi (I think?)

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If your dreams don't scare you, they are not big enough.

9/16 - 20 is the thread size that’s been used on bicycle pedals since the beginning of time... It’s a BSC as far as I know...

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08 Specialized Langster

Nick is of course spot on about bicycle pedals. 9/16" 20 tpi is BSCy thread and is also Unified Extra Fine (USA thread). In both cases, they are 60 degree thread form as opposed to other British Standard Thread forms that are typically 55 degrees angle. Since they are used for bicycle pedals, taps and dies are widely available in that size.

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Try doing this to yer fueller...........

a very quick and easy google search for 9/16 20 tpi and you get
https://www.amazon.com/20-Right-Left-Ha ... B075N48H1S

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Buell Ulysses XB12X 06/08

looks like it's a unified USA standard thread
https://www.ebay.co.uk/itm/2PCS-9-16-20 ... Sw0RBc66W1

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Buell Ulysses XB12X 06/08

Correct. It is a 9/16-20 UN thread per the machinists handbook.

And the others are correct about it being a bicycle pedal thread. Apparently, I'm the neighborhood bike repair guy so I have a set for cleaning up botched threads, not that it does you any good from here. Thanks to $2000+ bikes not coming with pedals anymore, it's amazing how many people fuck up their cranks when they try to install their $300 platform pedals. Righty tighty, eh?

I hope you're not asking because you need a nut. Difficult to find. None of my fastener sources at work have them and UN threads are common in oil and gas equipment, just not that small. Might have to make one.

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Bob Krzeszkiewicz
2012 XR1200X - 2011 Kawasaki Z1000SX - 1999 Buell X1

9/16"- 24 is actually UNEF. 20 is just UN.

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Bob Krzeszkiewicz
2012 XR1200X - 2011 Kawasaki Z1000SX - 1999 Buell X1

I stand corrected, sir

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Try doing this to yer fueller...........

Turns out my confusion has arisen from assuming that British Standard Cycle (BSC) thread is the same as Cycle Engineers Institute (CEI)! The Die I borrowed is etched as 'Cycle' as has 26tpi, this obviously must be CEI. You're advice about 'standard' cycle is spot on, as this is 20tpi.
I'm surprised that there's nothing mentioned in my Zeus book. Fire up the Myford!!!

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If your dreams don't scare you, they are not big enough.

NOT IN THE ZEUS BOOK

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Try doing this to yer fueller...........

I was just as surprised. UNEF is in there along with ME threads, which I've never come across, but the commonly used Cycle thread = nil!

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If your dreams don't scare you, they are not big enough.

A LOOOOONG time since I looked in a Zeus book! Longer than I care to remember.

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Try doing this to yer fueller...........