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 (413, 423, 433) of walls (41, 42, 43) or sections thereof, wherein the walls (41, 42, 43) 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 (413, 423, 433) of walls (41, 42, 43) or sections thereof, wherein the walls (41, 42, 43) 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.