The invention relates to a device (1) for the protection against electrical discharges of a conductive fixing element (4) of an aircraft, comprising a cap (2) made of non-conductive material and a washer (3) made of non-conductive material insulating the fixing element (4) from electrical discharges, said cap being an open receptacle with a cylindrical shape closed at one of its ends and open at the other end, comprising at the lower part of its inner face a thread (15), the washer (3) being retained by the fixing element (4), said washer (3) having a thread (5) on its outer face coupling with the complementary thread (15) in the lower area of the inner face of the cap (2), relative movements between the washer (3) and the cap (2) being prevented.