MJ thread to M thread interface?
MJ thread to M thread interface?
(OP)
I currently have a situation where a design engineer has specified a seriers of MJ threaded holes MJ2; MJ3 and MJ4 in an aluminium chassis and has specified M2; M3 and M4 screws as the mating fastener. My understanding of the MJ thread profile is that the root radius is increased (relative to the standard M designation) in order to reduce stresses in the threaded joint, and have never come across the deliberate mixing of thread forms before, niether have any of the other designers I have questioned on the subject, although the designer concerned claims that it is a standard practise to mix MJ and M, does any one else out there have any experience of or information pertaining to the correct application in this instance?





RE: MJ thread to M thread interface?
As such, M, MJ, UN, UNR, and UNJ thread profile compatibility is as follows, where "incompatible" in the following table means "interference occurs between nontruncated internal thread crest and shallow external thread root."
External Internal Compati-
thread thread bility
------- ------- --------
M M compatible
M MJ compatible
MJ MJ compatible
MJ M incompatible
UN UN compatible
UN UNJ compatible
UNR UN compatible
UNR UNJ compatible
UNJ UNJ compatible
UNJ UN incompatible