Abstract: A clip for sealingly connecting to a nipple, a pipe of a material that cold flows when subjected to prolonged mechanical pressure. The clip includes a constriction band intended to encircle the pipe and adapted for tensioning by a screw, which is rotatably mounted in a holder. One end of the band is secured to a nut travelling along the screw when the latter is turned, while the other end of the band coacts with one leg of a U-shaped spring for bringing the legs of the U-shaped spring together when the band is tightened around the pipe upon rotation of the screw. An indication element is held between the holder and the U-shaped spring for automatically indicating when predetermined relative travel of the legs of the spring has been attained.