NF VS. UNF

[The Cathedral]

I've stumbled upon an old thread gage, a 3/4-16 NF-2. NF was the precursor to UNF; unfortunately I cannot find anything that still lists the old threadforms (pitch dia, major/minor, etc) for the NF thread so I can compare it to the UNF standard. I want to see if this thread gage would still be usable or if it needs to be retired. 

 

Does anybody know where I can find these old dimensions, or can tell me what the differences are, if any? Thanks in advance. 

[specv]

http://gsi.nist.gov/global/docs/vps/csfiles/cs_24-30.pdf

 

Try that, otherwise I would send the gage to a calibration company for them to calibrate the gage  and certify it to UNF standards.

[The Cathedral]

That is exactly what I was looking for and confirms my suspicion that the gage is unusable. The tolerance opened up so technically the gage could still pass parts but it could also reject parts that are actually good. 

 

Thanks!

[GoetzInd]

 

 but it could also reject parts that are actually good. 

 

 

QC guy should like it then..  

[The Cathedral]

<<<<<<QA guy. Just moved in two weeks ago. Woooooo

[Allan]

Apparently the NF thread were changed to UNF in 1949; must be some old guages. 

 

There should be less than .0002 difference on PD according to these folks: http://www.ring-plug-thread-gages.com/ti-N-vs-UN.htm

 

 

 

[Tim Johnson]

There was a machine shop near me that had very old machining equipment. It was like a museum. Anyway the owner showed me his Machinery's Handbook. I don't remember what edition it was but it was a very fragile book. I was rifling though it (carefully) and came up to "Briggs Standard Pipe Treads". A search shows the  A.S.M.E. renamed the threads to National Pipe Taper (NPT) in 1919 so that handbook may have been the first edition.