A slit is cut into the top of the screw thread (2) between the two flanks (21), and the root of the thread groove is a wide recess (22, 23) of a shape scraped inward from the extended faces of the flanks.

By providing the wide recess, the slit at the top of the screw thread can be deep, and the flanks are easily elastically deformed, resulting in an enhanced spring-back effect.

apex of the fundamental triangle of a parallel screw thread

crest of a parallel screw thread

In addition, according to the invention, the flank crest (15) and the flank root (16) are rounded off.

The helical thread comprises a convex profile that is different than a thread profile of the thread of the pipe.

At least a portion of the micro-thread is spaced apart from the helical thread.

The feature that is not constant may be, for example, the spacing between turns of the thread, the height of the thread, the thickness of the thread, or the pitch of the thread.

The threads of the ring mate with the threads on the manifold.

The height of thread of the male pipe is less than the height of thread of the female pipe.

The steps on the box thread correspond generally in axial position with the steps on the pin thread.

A slit is cut into the top of the screw thread (2) between the two flanks (21), and the root of the thread groove is a wide recess (22, 23) of a shape scraped inward from the extended faces of the flanks.

The nut has internal threads complementary to the threads in the screw.

The diameter of the spongious thread of the screws is equal to or less than the diameter of the metric thread thereof.

The height of the thread profile of the male pipe is less than the height of the thread profile of the female pipe.