A filter cartridge comprising at least: - a filter element with a front end, a rear end and a fluid channel ; - a longitudinal axis extending through the front end of the filter element and through the rear end of the filter element , - a connector element being attached to the front end of the filter element , wherein the connector element has at least: o a forward-facing side facing away from the front end of the filter element in a forward direction and a rearward-facing side facing towards the front end of the filter element in a rearward direction , o a bottom , o a fluid-inlet port comprising a fluid inlet wall , which fluid inlet wall surrounds an inlet through hole in the bottom and extends from the bottom in the forward direction , o a fluid-outlet port comprising a fluid outlet wall , which fluid outlet wall surrounds an outlet through hole in the bottom and extends from the bottom in the forward direction , o a peripheral wall being attached to the bottom , o a first plain bearing surface facing in the forward direction, wherein the plain bearing surface is configured to limit an axial movement of the filter cartridge in the forward direction , wherein the first plain bearing surface is provided by a set of first forward facing sides of walls or sections thereof, wherein the walls extend from the bottom in the forward direction , characterized in that there exists a point P 1 which has the same distance d | RP | to all points on the first plain bearing surface. - a filter element with a front end, a rear end and a fluid channel ; - a longitudinal axis extending through the front end of the filter element and through the rear end of the filter element , - a connector element being attached to the front end of the filter element , wherein the connector element has at least: o a forward-facing side facing away from the front end of the filter element in a forward direction and a rearward-facing side facing towards the front end of the filter element in a rearward direction , o a bottom , o a fluid-inlet port comprising a fluid inlet wall , which fluid inlet wall surrounds an inlet through hole in the bottom and extends from the bottom in the forward direction , o a fluid-outlet port comprising a fluid outlet wall , which fluid outlet wall surrounds an outlet through hole in the bottom and extends from the bottom in the forward direction , o a peripheral wall being attached to the bottom , o a first plain bearing surface facing in the forward direction, wherein the plain bearing surface is configured to limit an axial movement of the filter cartridge in the forward direction , o a forward-facing side facing away from the front end of the filter element in a forward direction and a rearward-facing side facing towards the front end of the filter element in a rearward direction , o a bottom , o a fluid-inlet port comprising a fluid inlet wall , which fluid inlet wall surrounds an inlet through hole in the bottom and extends from the bottom in the forward direction , o a fluid-outlet port comprising a fluid outlet wall , which fluid outlet wall surrounds an outlet through hole in the bottom and extends from the bottom in the forward direction , o a peripheral wall being attached to the bottom , o a first plain bearing surface facing in the forward direction, wherein the plain bearing surface is configured to limit an axial movement of the filter cartridge in the forward direction , the first plain bearing surface is provided by a set of first forward facing sides of walls or sections thereof, wherein the walls extend from the bottom in the forward direction , characterized in that there exists a point P 1 which has the same distance d | RP | to all points on the first plain bearing surface. <EOS>