Acme vs Stub Acme Thread Form. Basic width of crest derivation.

[carpder]

I am trying to determine how the basic width of crest is derived in Stub Acme and Acme thread forms.

ACME:
Fcn= .3707*P
Height = .5*P

STUB ACME:
Fcn = .4224*P
H = .3*P

Does anyone know if/how these are derived?

See equations at bottom of this site. Just looking for how they were obtained.

http://www.amesweb.info/Screws/StubAcmeThreadedRodNutDimensions.aspx

Thanks!

 

[KENAT]

To be sure I'd get a hold of the relevant industry standard be it ASME or ISO or... for your location.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[3DDave]

They aren't derived. They are given. Note that none of the equations mentions the angle Alpha? I suspect with some trig one would find that the internal and external threads have the same face angle.