An assembly for making a positive locking fastener, said assembly comprising: - a nut, said nut having a tightening portion of angular period Θ about a major axis of said nut; and - a cap intended to engage with the nut and intended to receive a pin, said cap being substantially circular about a main axis and comprising: a locking portion at a first end, said locking portion determining an inner surface corresponding to a housing for engaging the tightening portion of the nut so that the main axis of said nut is substantially coincident with the main axis of the cap when said cap is in place on said nut; a locking portion at a second end, a side wall of said locking portion having at least one pair of through apertures adapted to receive the pin, said apertures of a pair being arranged symmetrically with respect to the main axis, along a direction defined by centres of said apertures of the pair, the apertures being similar in size with a height h along the direction of the main axis and a length defined by an angular sector φ for allowing movement of a straight portion of the pin in any of the at least one pair of apertures, said apertures being located at substantially the same height as said main axis; said blocking and locking portions being fixed and integral with each other and said cap being characterized in that the angular sector (φ) is equal to: φ = Θ / N where N denotes a number of pairs of openings. - a nut, said nut having a tightening portion of angular period Θ about a major axis of said nut; and - a cap intended to engage with the nut and intended to receive a pin, said cap being substantially circular about a main axis and comprising: a locking portion at a first end, said locking portion determining an inner surface corresponding to a housing for engaging the tightening portion of the nut so that the main axis of said nut is substantially coincident with the main axis of the cap when said cap is in place on said nut; a locking portion at a second end, a side wall of said locking portion having at least one pair of through apertures adapted to receive the pin, said apertures of a pair being arranged symmetrically with respect to the main axis, along a direction defined by centres of said apertures of the pair, the apertures being similar in size with a height h along the direction of the main axis and a length defined by an angular sector φ for allowing movement of a straight portion of the pin in any of the at least one pair of apertures, said apertures being located at substantially the same height as said main axis; said blocking and locking portions being fixed and integral with each other and said cap being characterized in that the angular sector (φ) is equal to: φ = Θ / N where N denotes a number of pairs of openings. a locking portion at a first end, said locking portion determining an inner surface corresponding to a housing for engaging the tightening portion of the nut so that the main axis of said nut is substantially coincident with the main axis of the cap when said cap is in place on said nut; a locking portion at a second end, a side wall of said locking portion having at least one pair of through apertures adapted to receive the pin, said apertures of a pair being arranged symmetrically with respect to the main axis, along a direction defined by centres of said apertures of the pair, the apertures being similar in size with a height h along the direction of the main axis and a length defined by an angular sector φ for allowing movement of a straight portion of the pin in any of the at least one pair of apertures, said apertures being located at substantially the same height as said main axis; said blocking and locking portions being fixed and integral with each other and said cap being characterized in that the angular sector (φ) is equal to: φ = Θ / N where N denotes a number of pairs of openings.