Abstract: In order to guarantee the sealing quality of a joining between a pipe socket and a tube by means of a clamp pressing a tube on a pipe wall, where the press-on power to be exercised by the tube clamp will act as uniformly as possible all over the total pipe circumference and cause no damage to the tube, it is suggested that the clamp is an open tube clamp being operative by its inner clamping power over a relatively wide-ranged press-on surface, being moved into its acting position by a tool overcoming the clamping power, and where an almost uniform pressing is provided extending over the total press-on surface (F) by a cross section increasing from the open ends (E1, E2) in direction to the clamping dead center (R).