A protection system for a threaded fastener, the protection system comprising - a threaded fastener mounted through two flanges (2,3), - a sleeve and either - two nuts and two end caps or - one nut and one end cap and one component with threaded hole, wherein the sleeve together with either the two end caps or together with the one end cap and the one threaded hole of the component form an enclosure around the threaded fastener, and a sealing ring is provided, which sealing ring comprises an inner sealing that seals against the sleeve and an outer sealing that seals against one end cap such that the enclosure forms a cavity containing part of the threaded fastener that engages with the nut or the threaded hole, wherein the cavity is completely sealed from the environment, characterized in that wherein the threaded fastener is fitted with an extender enabling use of a fastener that is longer than the combined thickness of the flanges (2,3), and wherein each sealing (12,16) is in the form of an O-ring, and wherein a hardened washer is mounted between the nut and the sealing ring and, wherein an insulating washer is mounted between the sealing ring and the extender, and wherein the end cap comprises a threaded ring and an end cap cover and the threaded ring 14 forms a seal with the outer sealing. - a threaded fastener mounted through two flanges (2,3), - a sleeve and either - two nuts and two end caps or - one nut and one end cap and one component with threaded hole, wherein the sleeve together with either the two end caps or together with the one end cap and the one threaded hole of the component form an enclosure around the threaded fastener, and a sealing ring is provided, which sealing ring comprises an inner sealing that seals against the sleeve and an outer sealing that seals against one end cap such that the enclosure forms a cavity containing part of the threaded fastener that engages with the nut or the threaded hole, wherein the cavity is completely sealed from the environment, characterized in that wherein the threaded fastener is fitted with an extender enabling use of a fastener that is longer than the combined thickness of the flanges (2,3), and wherein each sealing (12,16) is in the form of an O-ring, and wherein a hardened washer is mounted between the nut and the sealing ring and, wherein an insulating washer is mounted between the sealing ring and the extender, and wherein the end cap comprises a threaded ring and an end cap cover and the threaded ring 14 forms a seal with the outer sealing. - two nuts and two end caps or - one nut and one end cap and one component with threaded hole, wherein the sleeve together with either the two end caps or together with the one end cap and the one threaded hole of the component form an enclosure around the threaded fastener, and a sealing ring is provided, which sealing ring comprises an inner sealing that seals against the sleeve and an outer sealing that seals against one end cap such that the enclosure forms a cavity containing part of the threaded fastener that engages with the nut or the threaded hole, wherein the cavity is completely sealed from the environment, characterized in that wherein the threaded fastener is fitted with an extender enabling use of a fastener that is longer than the combined thickness of the flanges (2,3), and wherein each sealing (12,16) is in the form of an O-ring, and wherein a hardened washer is mounted between the nut and the sealing ring and, wherein an insulating washer is mounted between the sealing ring and the extender, and