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midtown1-Visitor
1-Visitor
October 25, 2017
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What does "H-tapered" mean on NPT note?

  • October 25, 2017
  • 3 replies
  • 7687 views

On the drawing for designating an NPT thread, it has "H-tapered."  What does that mean?  I've checked the Machinery's Handbook and online but can't find anything that explains it.  When creating the thread in the model, there's a Class with a Value set to H, but I think that's a default setting when choosing a 1/4-18 thread.  I'd rather not purchase ANSI/ASME 1.20.1 to find out.

Best answer by dschenken

Check

https://en.wikipedia.org/wiki/National_pipe_thread and the references on the page.

 

Class 1 and 2 appears to apply to NPTF threads.

http://www.ring-plug-thread-gages.com/ti-NPT-vs-NPTF.htm

 

I agree with@BillChapmanthat it's an error by PTC.

3 replies

B
23-Emerald III
BenLoosli23-Emerald III
23-Emerald III
October 25, 2017

Someone on practicalmachinist.com suggested that the H may refer to it being for a hose fitting. That way the machinist knows to use a tapered reamer before tapping.

B
BillChapman13-Aquamarine
13-Aquamarine
October 25, 2017

I think that this is just a bad note from PTC out of the box. Both the -H and the "tapered" designation is off.

NPT

N=National

P=Pipe

T=Taper

so the "tapered" in the "H-tapered" portion of the note is redundant and is not needed.

 

The full callout as I know it is:

1/4-18 NPT 

 

You can specify class 1 or class 2 which has to do with specific inspection of the root and crest of the thread.  In this case the full callout is:

 

1/4-18 NPT-1 or 1/4-18 NPT-2

    D
    dschenken1-VisitorAnswer
    1-Visitor
    October 25, 2017

    Check

    https://en.wikipedia.org/wiki/National_pipe_thread and the references on the page.

     

    Class 1 and 2 appears to apply to NPTF threads.

    http://www.ring-plug-thread-gages.com/ti-NPT-vs-NPTF.htm

     

    I agree with@BillChapmanthat it's an error by PTC.

    M
    midtown1-VisitorAuthor
    1-Visitor
    October 30, 2017

    I'm going with a bad callout by PTC.

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