in reference to fig1 to 3 , we will now describe a first embodiment of the invention . an assembly according to the invention comprises two nuts 3 and 5 . nut 3 is called the primary nut , while nut 5 is called the secondary nut . the assembly 1 has a longitudinal axis x . it is capable of being mounted on a screw not shown and extending according to the x - axis . the primary nut 3 has , on an external surface , means 31 for connection with an adjustable tailplane according to primary means , neither of which are shown , in the context of a thsa actuator for an aircraft . at one of its ends , the primary nut 3 has a collar 93 . this collar 93 comprises orifices 33 capable of receiving a pin 9 , which will be described below . the primary nut 3 can be a ball or roller nut intended to be mounted on a so - called ball or roller screw , respectively . the secondary nut 5 has , on an external surface , means for connection 59 with the adjustable tailplane via so - called secondary means , neither of which are shown , in the context of a thsa actuator for an aircraft . in an internal bore passing through along the x - axis , the secondary nut 5 has a threading 51 . this threading is complementary in its shape to the threading of the screw on which it is intended to be mounted , assembled to the primary nut 3 . this threading 51 , although complementary to the threading of the screw on which it is intended to be mounted , is of a size so that once it has been mounted , the threading 51 of the nut has a play with the threading of the screw on which it is mounted . at one of its ends , the secondary nut 5 has a collar 54 capable of being received by the collar 93 of the primary nut 3 , as shown in fig2 . the collar 54 has openings 55 capable of receiving , when the secondary nut 5 is mounted on the primary nut 3 , the aforementioned pin 9 . angularly , in line with said openings 55 , the secondary nut 5 comprises protuberances 53 extending radially outwardly , projecting from the external surface and in which a through - hole is provided , substantially parallel to the x - axis of the secondary nut 5 . the through - hole is capable of receiving a link 7 , which will be described below . it should be noted that the orifices 33 of the collar 93 of the primary nut 3 , the openings 55 of the collar 54 of the secondary nut 5 , as well as the protuberances 53 , are in this case , as shown , in pairs located diametrally opposed with respect to the x - axis of the assembly 1 . the assembly 1 also comprises a wedge 11 inserted between the primary nut 3 and the secondary nut 5 . the role of this wedge 11 is to ensure the precise relative positioning between the primary nut 3 and the secondary nut 5 . the thickness of the wedge 11 is calculated so that , once the two nuts have been mounted on the screw not shown , a play appears between the threading 51 of the secondary nut 5 and the threading of the screw on which the assembly 1 is mounted . this play makes it possible , in normal , effective operation of the assembly 1 mounted on the screw , for there to be no contact between the threading 51 of the secondary nut 5 and the threading of the screw . the wedge 11 can be obtained directly by calculation or adjusted , for example , by machining , by pealable means or by grading , or any other means enabling the required play to be obtained . the wedge 11 is , as shown in fig2 , located between an end surface of the collar 54 and a base of the bore delimited by the collar 93 of the primary nut 3 . alternatively , the nut 11 is located between an end surface of the collar 93 and an edge substantially perpendicular to the x - axis of the secondary nut 5 located at the foot of the collar 54 . in addition , the assembly 1 according to the invention comprises a pin 9 associated with a link 7 . the pin 9 includes a tail 91 as well as a threaded opening perpendicular to the tail 91 of the pin 9 . the pin 9 is mounted radially with respect to the x - axis in the orifice 33 of the collar 93 of the primary nut 3 , through which it passes , and into the opening 55 formed in the collar 54 of the secondary nut 5 , which is then mounted on the primary nut 3 , so that the openings 55 and the orifices 33 are opposite one another . with the pin 9 thus mounted , the threaded orifice perpendicular to the tail 91 of the pin 9 is located opposite the through - hole of the protuberance 53 . then , a link 7 is inserted into said orifice , as shown in fig2 . the link 7 has a general rotating form and successively comprises a head 7 of which the diameter is greater than a diameter of the through - hole of the protuberance 53 in which it is received , then a smooth cylindrical rotating portion 73 of which the diameter is slightly smaller than the diameter of the through - hole in which the link 7 is received , then a portion 71 having a reduced diameter , and finally , a threaded portion 75 capable of being screwed into the threaded orifice of the pin 9 . the portion 71 of the link 7 has a cross - section sized so that , when a predetermined pulling force is exerted between the threaded portion 75 and the head 7 , the portion 71 breaks . this breakage occurs after a predetermined extension according to the cross - section of the portion 71 subjected to said predetermined pulling force . the mounting of the assembly 1 includes the primary nut 3 , the wedge 11 and the secondary nut 5 , which are stacked one on top of another . the orifices 33 are placed opposite openings 55 in order to enable pins 9 to be mounted . finally , the links 7 are inserted into the through - hole of the protuberances 53 and are screwed into the threaded orifice of the pins 9 so as to hold the stack of the primary nut 3 , the wedge 11 and the secondary nut 5 during normal operation . however , the pulling force caused by the tightening of the links 7 in order to hold the stack should be negligible with respect to the predetermined pulling force for breaking the portion 71 of the links 7 . we will now , in reference to fig4 , describe a second embodiment of an assembly according to the invention . we will simply describe the differences between this second embodiment and the first embodiment of the invention described above . the main difference lies in the collar 90 of the primary nut 3 , which is differentiated from the collar 93 of the primary nut 3 of the preceding embodiment . the collar 90 has protuberances 95 projecting outwardly and radially with respect to the x - axis . these protuberances 95 make it possible to eliminate , in this embodiment , the pins 9 of the first embodiment described above . these protuberances 95 therefore have a threaded orifice capable of receiving , by screwing , the threaded portion 75 of the link 7 . the wedge 11 is mounted between the secondary nut 5 and the primary nut 3 according to the alternative mounting described in the first embodiment : between an end surface of the collar 95 and an edge of the nut 5 extending radially outwardly and perpendicularly to the x - axis at the foot of the collar 54 . in addition , the assembly 10 comprises retaining means 53 . these retaining means 53 make it possible to hold the head 7 and the portion 73 of the link 7 in place when the portion 71 of the link 7 is broken under the effect of a predetermined pulling force . this prevents , in the event of a breakage , said portion of the link 7 from damaging , by breaking away , other components of the aircraft on which the assembly 10 is installed . in the two embodiments , when there is a failure of the primary nut 3 leading to a loss in connection between the primary nut 3 and the screw , there is a change in the flow of forces originating in the adjustable tailplane . first , according to the loss in connection between the primary nut / screw , the forces originating from the adjustable tailplane always pass through the primary means to the primary nut 3 , then via the links 7 to the secondary nut 5 . the play between the threadings of the secondary nut and the screw is then taken up , and the threadings come into mutual contact . and the forces are transmitted to the screw by the secondary nut 5 . second , once the forces originating from the adjustable tailplane reach a value greater than the pulling effect causing a breakage of the portion 71 of the links 7 , the latter break , detaching the secondary nut 5 from the primary nut 3 . then , the forces originating from the adjustable tailplane pass directly via the secondary means to the secondary nut 5 , and from there to the screw .