Abstract: A filter ring is described for insertion in ring-shaped apertures or openings of the wall of hollow bodies containing or through which gases or liquids flow. In its wall surrounding a hollow space, the ring has a longitudinal slit extending parallel to the axis of the ring along the entire axial length of the ring, the wall portions of the ring located to both sides of the slit being joined with one another by a snap lock. In accordance with the invention, this snap lock has at least two projections which are arranged in the one wall portion of the ring in an axial direction and which are snappable into grooves arranged equally adjacent to one anotehr on the other wall portion. The projections and grooves extend over the entire thickness of the ring wall and have side surfaces undercut in the joint direction and engage one another from behind.