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UNJF vs UNF internal threads


mchris77
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I have a 1/2-20 UNJF-3B thread to make. I've been reading specs all morning and from what I can tell a UNF and UNJF thread are the same for an internal hole. With the exception of the UNJF having a slightly larger minor dia. So I should be able to use a 60 deg single point threading tool without issue. Can anybody confirm or deny this?

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quote:

With the exception of the UNJF having a slightly larger minor dia. So I should be able to use a 60 deg single point threading tool without issue. Can anybody confirm or deny this?

That is correct. And use the same 1/2-20-3B gages.

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"J" style threads are mostly used in Aerospace.

 

All the "J" means is a controlled root radius which is also a larger radius, than the standard UN threads root radius on MALE threads.

 

So when creating a "J" MALE thread the correct screw cutting, or thread mill must be used to create the correct root radius.

 

When creating a "J" female thread all that needs to be done is to create a larger Minor diameter to clear the larger root radius on the male thread. Standard UN insert can be used.

 

The larger root radius on the male thread creates a stronger male thread.

 

HTH

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