Abstract: To connect the end of a flexible collar (11) on a flexible wall (12) that belongs, for example, to a containment insulator, one part of that wall is mounted around a circular opening provided for that purpose on a fixed inner ring (18). A toric joint (20), which rolls between two grooves, (18c, 18b) formed on the ring (18) when the rigid outer ring is put into place (22) covering the end of the collar (11), blocks the wall (12) in the groove (18b). An immobilizing ring (24) is then placed in the other groove (18c) to keep the outer ring (22) from escaping.