2 Questions on UNJF threading 3

[NCYankee]

1st post.

Some explanation first. Our design engineer recently made a change in the type of stud used to join the cover (lid) to a transmission main case. The stud has two threaded areas of different lengths, both with a 5/16-24 UNJF-3A threading callout. As the stud is put in, it goes through a thru-hole in the lid, and is supposed to go into a 5/16-24 UNF-2B threaded hole on the main case. After the stud is installed a lock nut goes on the bottom side (main case side)and tourqued down, and another nut is put onto the top side, and also tourqued down.

My first question is, will the UNJF-3A exterior thread fit into the UNF-2A threaded bolt hole, and if not, what will it fit into. My DE seems to think that there will be clearance to allow the fit, but I'm not so sure, and since our company is pretty small, we don't have the resources for me to buy all the specs we really need.

My second question is pretty straight forward. What is the best way to check the UNJF threads? Would it be a threaded ring gage, thread micrometers, 3-wire method, or something else?

Thanks in advance for any help.

 

[ewh]

As for the first part of your question, this may be related - thread725-205229
I am also still interested in knowing if this is proper.

"Believe it if you need it or leave it if you dare." - Robert Hunter

 

[NCYankee]

I saw that post, but was still confused as there were two different things said there. If you follow the link posted (

http://www.tcnj.edu/~rgraham/barrett/manual1-B.html

), you're told in the table that UNJ Class 3A mates only with UNJ internal threads. However, someone else posted that they thought that it would fit and would reply if it didn't. They did not reply, which I infer means that they were able to fit a UNJ - 3A bolt into a UN - 2B bolt hole. As I said...cofnusing.

 

[ewh]

... and it supposedly works only one way - a un stud will not fit into a unj hole.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[NCYankee]

Still looking for a more definitive answer for my first question, and nobody's touched the 2nd one. Any help would be very welcomed.

Thanks to ewh for his responses.

 

[CoryPad]

UNJ 3A needs a UNJ mating thread.

This is the best way to check threads:

http://www.johnsongage.com/pr_is_external.shtml

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ewh]

Could you expound on that, Cory? I know that I have seen UNJ male threads installed into un holes without apparent problems, though I don't remember the thread class.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[CoryPad]

ewh,

Class 2A/2B threads are for general use and have an allowance designed in. This allows an external UNJ to mate with an internal UN. Class 3A/3B are for precision fit and do not have an allowance, so you need UNJ to UNJ.

NCYankee,

You can get MIL-S-8879C SCREW THREADS, CONTROLLED RADIUS ROOT WITH INCREASED MINOR DIAMETER, GENERAL SPECIFICATION FOR for free at ASSIST:

http://assist.daps.dla.mil/quicksearch/

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ewh]

In the situation to which I was referring, we had to use an AN hydraulic fitting (which had a UNJ thread), but the strength of a UNJ thread was not required. A UN thread was determined to have sufficient strength and was more economical to produce. Physically, a UNJ male fitting DID install into a UN hole with no adverse effects (for our purposes).
If the inherent strength of the UNJ thread is necessary, then Cory is correct, mate it with the corresponding UNJ thread.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[ewh]

Thanks for the clarification, Cory!
That helps me understand it much better, and makes sense.
I no longer have the data that we used, and it may well have been 2A, not 3A.


Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]