thread class question...

[PaulieUMF]

Occasionally I run into a thread call out that is missing the thread class. I've always gone on the assumption that it would be a class 2 thread, but I can find no hard and fast rule about this. Any ideas?? Thanks!

 

[ctopher]

I always call out the class. I have had machine shops say they need it.

https://www.natool.com/wp-content/uploads/2019/06/classes_of_fit_web_catp101-102.pdf

https://amesweb.info/Screws/asme-imperial-un-thread-calculator.aspx

Usually when someone does not call it out, they don't know much about threads.
I'm not sure of a spec that indicates it needs to be there. But, better to have it than not.

ctopher, CSWP
SolidWorks '17
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[chez311]

You haven't found one since there is none. Unless the thread dimensions are explicitly defined on the drawing (pitch/major/minor) if no thread class is specified then theres no way to tell what tolerances should be applied to the thread dimensions.

If I'm to play devils advocate, Class 2 is probably a safe bet since thats the most common but in truth there is no way to tell and there is no "default". If your threads are coated such designations become even more important.