Abstract: A clamping ring and closure made of plastic material comprising a closure head integrally formed at one end of a clamping ring of U-shaped section which has a passage into which can be inserted the opposite end of the clamping ring which is in the form of a tongue. Interlocking teeth are provided on the side edges of the tongue and on the side walls of the passage. The side walls of the closure head are connected together by non-overlapping spacer webs and the sawteeth on the two side walls are disposed opposite one another at the points of attachment of the spacer webs. The locking teeth are dispoed on the tongue at an acute angle in relation to the longitudinal axis of the clamping ring and at their end surfaces they extend substantially perpendicularly to the longitudinal axis. Along one side edge of the tongue there is formed a reinforcing strip whose inner side is provided with sawteeth while the locking teeth formed on this side edge are widened over its outer side.