# Cutting M8  x 1.25 threads on 5/16 rod



## RHayes (Feb 27, 2017)

I would like to cut some  M8 x 1.25 threads on the end of  a 5/16" rod (1145 cold formed)  using a die. 
 8mm converts to .3149 and 5/16 converts to .3125.  This is not ground and polished shafting so the od could be a couple thousanths less.  I'm not too good at calculating thread minimum and maximum diameters and would like to know if there is adequate diameter for a 75% or better thread.


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## Tony Wells (Feb 27, 2017)

It will be fine.


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## strantor (Feb 27, 2017)

This ref says 8mm bolt is 7.76mm to 7.972mm. So I think you're good.


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## darkzero (Feb 27, 2017)

The major dia max & min for a M8x1.25 6g thread is .313"-.306".


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## Wreck™Wreck (Feb 27, 2017)

Way more then needed, minimum Major Diameter according to the ANSI standards for a 3A is .304.

If you are truly concerned about the thread use the Maximum Major Diameter, Min. Minor Dia. and Max. PD on the external thread.

Use the Max Minor Dia,, Max Major Dia. and Max PD on the internal thread, this will prove difficult at home however.

The basic numbers may may be found here,  buy some ring and plug gauges, Good Luck

http://www.engineersedge.com/screw_threads_chart.htm

This is an excellent primer on basic thread design, worth a read.
https://www.fastenal.com/content/feds/pdf/Article - Screw Threads Design.pdf


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## RHayes (Feb 27, 2017)

Thanks so much.  I appreciate the information and should be able to figure this out in the future.


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