An oil filtration system comprising - an oil filtration unit, - an oil filter having a central opening extending along a central axis of the oil filter and having a filtering material, - the oil filtration unit being provided with at least one first physical structure (18,18',18") having a non-circular first cross-sectional shape and a predefined longitudinal length (x) in relation to the central axis of the oil filtration unit, - the oil filter being provided with at least one second physical structure (23,23',23") having a non-circular second cross sectional shape and a predefined longitudinal length (y) in relation to the central axis of the oil filter and - an inner periphery of the second physical structure (23,23',23") being arranged to mate with the outer periphery of the first physical structure (18,18', 18") allowing the oil filter to reach its correct insertion position in the oil filtration unit by the second physical structure (23,23',23") surrounding the first physical structure (18,18',18") at least partly, - where at least one of the end surfaces (28,29,31) of the oil filter relative to the central axis of the oil filter comprises the at least one second physical structure (23,23',23"), characterized in that - the second physical structure (23,23',23") forms part of the filter by comprising a filtering material suitable for oil filtration similar to the filtering material of the oil filter and as such is an active filtration component in the filtering process. - an oil filtration unit, - an oil filter having a central opening extending along a central axis of the oil filter and having a filtering material, - the oil filtration unit being provided with at least one first physical structure (18,18',18") having a non-circular first cross-sectional shape and a predefined longitudinal length (x) in relation to the central axis of the oil filtration unit, - the oil filter being provided with at least one second physical structure (23,23',23") having a non-circular second cross sectional shape and a predefined longitudinal length (y) in relation to the central axis of the oil filter and - an inner periphery of the second physical structure (23,23',23") being arranged to mate with the outer periphery of the first physical structure (18,18', 18") allowing the oil filter to reach its correct insertion position in the oil filtration unit by the second physical structure (23,23',23") surrounding the first physical structure (18,18',18") at least partly, - where at least one of the end surfaces (28,29,31) of the oil filter relative to the central axis of the oil filter comprises the at least one second physical structure (23,23',23"), characterized in that - the second physical structure (23,23',23") forms part of the filter by comprising a filtering material suitable for oil filtration similar to the filtering material of the oil filter and as such is an active filtration component in the filtering process. - the second physical structure (23,23',23") forms part of the filter by comprising a filtering material suitable for oil filtration similar to the filtering material of the oil filter and as such is an active filtration component in the filtering process.