UNJC and UNJF threads.
"J" threads are made in both external and internal forms. The external thread has a much larger root radius than the corresponding UNC, UNR, UNK, or UNF threads. This radius is mandatory and its inspection is required, whereas no root radius is required on UNC, UNF, or UNEF threads. Since the larger root radius increases the minor diameter, a UNJF or UNJC fastener has a larger net tensile area than a corresponding UNF or UNC fastener. This root radius also gives a smaller stress concentration factor in the threaded section. Therefore, high-strength (180 ksi or more) bolts usually have "J" threads.
I am using an NAS577 self-locking barrel nut with unjf threads in an allplication where I am monting a bullet antenna to the nose of an aircraft...if that helps at all?
Yes, there is such a thing as an internal UNJ thread. The sole modification to the internal thread form/dimensions (when compared to a “standard”, “non-J” thread) is a small increase in the thread minor diameter (the “pre-tap” or “pre-thread-cutting” diameter) to prevent potential interference of the increased diameter, radiused external UNJ thread root with the internal thread.
