Hollow body assemblies

A hollow body assembly comprising:

• at least first and second individual elements, having longitudinal axes, adapted for connecting together to form said hollow body, at least one of said elements having a tongue on its connecting surface and the other element having a groove on its connecting surface for mating with said tongue thereby forming an annular cavity between said tongue and the surface of said groove when said individual elements are connected, the axial distance between said tongue and the surface of said groove being greater near the center of said tongue than at the edges thereof;
• first and second circumferential flanges disposed on said first and second elements, respectively, at said connecting surfaces, each of said flanges having a transverse outer face perpendicular to said longitudinal axis and an inner face, said inner face being oblique to said transverse direction so that the width of said flange in the axial direction increases toward the base of said flange;
• and
• a circumferential ring surrounding said first and second flanges and having an inner channel, said ring having side edges for gripping the oblique surfaces of said first and second flanges when said first and second elements are connected, the distance between said side edges when said ring is in its unstressed condition being less than the distance between the base points of the oblique surfaces of the flanges.