UN VS UNJ threads

[mike-sid]

I'm threading a part for my mill. My full forming carbide inserts for my lathe are labeled 24 UNJ ( 16 ER 24 UNJ) all my other inserts are just UN. Like 20 UN (16 ER 20UN). What's the difference between UN and UNJ threads?

[arvidj]

More than you might want to know about it ...

http://www.threadcheck.com/whats-the-j-i...nicalinfo/

... or maybe nothing that you really wanted to know ...

[mike-sid]

Just right. Good to know, how and why. but different they are.