a container and complementary sealing lid both of which are of plastic , in which the container has a sealing bond on its wall around its upper peripheral edge of two different radii , the larger one on the outside , and the lid has a u - shaped peripheral sealing channel with inner and outer side walls and an upper wall joining the side walls . the inner surface of the upper wall is formed with areas of two different radii with the larger on the inner surface of the channel outer side wall and the container sealing bead and lid sealing channel being sized so that sealing engagement occurs between the bead and channel smaller radii areas and there is a clearance between the other parts of the bead and channel to aid in fastening and removing the lid .