Abstract: A joint is connected to a tube and includes a joint body, nut, and ring. The joint body has a tube coupling part and a main body thread part. The nut has a nut thread part and a constricted diameter part. The ring is arranged in a space radially inward of the nut thread part. The ring abuts an abutted part of the nut. The ring has a Young's modulus greater than the tube. The ring has a curved surface part at least at a radially inward portion of the ring axially on the joint body side, the curved surface part bulging radially inward of the ring and axially toward the joint body side. A maximum thickness of the ring in a radial direction is defined as 2r, an axial length of the curved surface part of the ring is defined as h, and ?=h/r being 0.5 to 1.2.

Abstract: An apparatus comprises a first number of splines located near a first end of a first joint section and a second number of splines located near a second end of a second joint section. The first number of splines extends in an axial direction of the first joint section and spans a circumferential surface of the first joint section. Each of the first number of splines has a base, a tip, and a pair of flanks that extends from the base to the tip and forms an acute angle. Each of the first number of splines are configured to be received between adjacent pairs of splines in the second number of splines as the first end of the first joint section and the second end of the second joint section are joined.

Abstract: A polymeric device for protection of the connecting pipe coupling contains a stepped bushing having a medium part with an increased diameter and two lateral parts with a smaller outside diameters, which is installed between end faces of pipes with a conic thread, and connected by means of a coupling and having sealing rings made of an elastomer, which are on parts of the bushing with the small diameter. The device has an additional stepped bushing, and the first stepped bushing has a constant outside diameter and two parts with small and large internal diameters, and the second stepped bushing has a constant internal diameter and two parts with small and large diameters.