2 Questions on UNJF threading
2 Questions on UNJF threading
(OP)
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.
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.





RE: 2 Questions on UNJF threading
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
RE: 2 Questions on UNJF threading
RE: 2 Questions on UNJF threading
Believe it if you need it or leave it if you dare. - Robert Hunter
RE: 2 Questions on UNJF threading
Thanks to ewh for his responses.
RE: 2 Questions on UNJF threading
This is the best way to check threads:
http://www.johnsongage.com/pr_is_external.shtml
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: 2 Questions on UNJF threading
Believe it if you need it or leave it if you dare. - Robert Hunter
RE: 2 Questions on UNJF threading
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: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: 2 Questions on UNJF threading
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. - Robert Hunter
RE: 2 Questions on UNJF threading
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. - Robert Hunter