UNJ series thread

[Dave K]

First time I've come across a UNJ-series thread outside of the aerospace world...

...the center lock, single wheel nuts that we purchase have a UNJ internal thread. Looking at what info I can find, and going from memory, I'm trying to confirm that a UN series external thread will work in a UNJ series internal thread, but a UNJ series external thread will not work in a UN series internal thread. This because the UNJ external has the larger root radius, and would cause interferrence, but the UNJ internal thread only has a larger minor diameter.

Can anyone confirm this?

-Dave
Everything should be designed as simple as possible, but not simpler.

 

[EngJW]

I wrote down some notes on this a few years ago and it was pretty much the way you have stated it. Unfortunately I didn't write down the source other than the J thread was used on NAS bolts and some connecting rod bolts.

There is also a forum here on fastener engineering in the Structural Engineers section. They might be of more help.

 

[EngJW]

Just found a copy of the International Fasteners Institute Handbook.

The larger J radius is only used on the external thread. The J nut has the larger minor dia to clear. A J nut and bolt use Class 3 threads to make up for the loss in engagement area.

A J nut will fit a UN bolt but they suggest caution because of the loss in area. I think most bolts are already Class 3 however.

Even though a J nut is supposed to be used with a J external thread, they say that many users have used standard nuts without any problem.

Hope this helps.

 

[Dave K]

Thanks. I'm going to suggest we use a UNJ series external thread, but offer the info that a standard UN series could be used.

Much appreciation...I'll check out that fastener forum too.

-Dave

-Dave
Everything should be designed as simple as possible, but not simpler.