MJ thread is a kind of thread with high fatigue strength. It is called aerospace thread by International Organization for Standardization. It is mainly used in aircraft and spacecraft products. Therefore, its basic tooth shape is different from that of metric common thread (M).

The ordinary thread is the ordinary round thread, the tooth Angle is 60°, the self-locking performance is good, the thread shear strength is high, the small path of the thread pair has a gap, the root of the external thread allows a larger rounded Angle to reduce the stress concentration. National standard: GB/T192~197-2003.

Basic shape of ordinary (M) thread

Basic shape of MJ thread

The basic tooth height of MJ thread is lower than that of ordinary thread. The difference between the design tooth shape of MJ external thread and the basic tooth shape is that the arc of the tooth bottom is a continuous smooth curve, and the radius of the arc of any part of the curve should not be less than 0.15011P. The design tooth shape of internal thread is the same as the basic tooth shape.

MJ threads have the same basic deviation, tolerance class, top diameter tolerance and middle diameter tolerance as normal threads. However, MJ threads specify the middiameter equivalent of the sum of thread pitch, tooth Angle, helix, taper and roundness errors, and other errors affecting thread shape, and shall not be greater than half of the middiameter tolerance. This introduces the concept of thread single diameter and action diameter, we will not expand the description.