UNJF vs UNF Threads – What is the difference?

Q: I have a customer requesting a UNJF thread for his Aerospace application. How are these different from a UNF thread?
A: This is a great question as UNJ threaded bolts are not interchangeable with a standard UN, UNC, or UNF nut. An internal UNJ thread will assemble to a standard UN external thread but the reverse is not the same due to the interference at the minor diameter. The UNJ external threads have a larger root radius than a standard thread pitch. This ultimately improves the tensile stress area of the fastener, making the threads stronger. Many aerospace applications use these types of threads because of the increased strength.
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