[ 0034 ] fig1 shows a metal ribbon 9 covered on both faces with a layer 15 of a metal that is a good electrical conductor , as can be seen in fig1 a . in the remainder of the description , the expression “ good electrical conductor ” refers to any metal that is a significantly better conductor than the metal of the ribbon . at least the central strip cs of the ribbon is covered by the layer 15 and regularly spaced openings 12 are punched into the central strip , as can be seen in fig2 . the openings can optionally be made before the ribbon is covered with the layer 15 of metal that is a good conductor , as explained below . it is assumed in the remainder of the description that the whole of the surface of the ribbon 9 is covered during the metal - plating operation and that the openings 2 are formed after metal - plating . the metal of the ribbon is an alloy of beryllium and bronze , for example , which is a relatively poor electrical conductor , and the metal - plating process is electrolytic galvanization in a bath of silver , for example . if the whole of the ribbon is galvanized , the edges of the ribbon are covered with a layer joining its two faces , like the layer 15 s shown in fig1 a . as shown in fig2 the openings 2 are formed in the metal - plated ribbon from fig1 a with an original regular pitch d 1 in the direction of the longitudinal axis a of symmetry of the ribbon , to form a discontinuous central strip cs of blades 3 whose longitudinal ends 31 and 32 are attached to two continuous edge strips es 1 and es 2 of the ribbon . it is preferable for the openings to be relatively narrow at their waists , which in this embodiment are along the longitudinal axis a of symmetry of the ribbon , in particular to obtain as small as possible an original pitch d 1 for a given blade width d , and also to limit the quantity of scrap material . the width d of each blade is preferably greater than approximately 80 % of the original pitch d 1 , which amounts to saying that the width of an opening at its waist is at most equal to approximately 20 % of d 1 , since this width at the waist is equal to d 1 - d . for a particular blade width d , it is not desirable for the original pitch d 1 of the openings to be much greater than d , as this would impose the use of a longer metal - plated ribbon and increase the width of the openings , which would represent a fabrication cost penalty . furthermore , with a pleating operation producing pleats protruding from the same side of the ribbon , as described below , the height of the pleats increases with the original pitch d 1 , although it is not desirable to have pleats that are too large , which could impede the fitting of the contact strip to the connector for which it is intended . the two edge strips es 1 and es 2 of the ribbon are externally notched to form tongues 4 that are used to connect the contact strip with a portion of the connector for which it is intended . in this embodiment the blades 3 are symmetrical with respect to their longitudinal axes a t , which are perpendicular to the longitudinal axis a , but a design could be envisaged that is not perfectly symmetrical , adopting a slightly asymmetrical shape of opening . conventionally , the blades are then subjected to a twisting operation about their longitudinal axis to pivot them relative to the plane of the ribbon so that the two faces of each blade form respective contacts 3 a and 3 b protruding on each side of this plane , as can be seen in the first portion of fig3 . this twisting operation is conventionally accompanied by bending the two edges of each blade in at least one longitudinal plane perpendicular to the plane of the ribbon to form on each face of a blade at least one contact area in which the current flows between the blade and a portion of a connector . in the remainder of the description , it is to be understood that a contact 3 a or 3 b comprises at least one contact area . in a fabrication method according to the invention , it is generally preferable , for cost reasons , for the operations of cutting out the blades and the tongues , twisting and bending the blades , and pleating the continuous edge strips of the ribbon to be carried out during a continuous process performed in a single installation . this is because it is less costly , in particular in terms of labor costs , not to have to reinstall or adjust the ribbon between operations . this is why it is generally preferable for the metal - plating operation to be carried out right at the beginning of the fabrication method according to the invention . furthermore , it must be noted that when punching a solid metal - plated ribbon , as shown in fig1 a , electrical conduction between the two layers that cover the two faces of the blades of the ribbon is effected only through the thickness of the metal of the ribbon . this is because a blade cut by a punch does not have on its edges a metal layer joining its two surface layers , such as the layer 15 s that can be seen on the edge of the ribbon in fig1 a . the metal of a contact strip ribbon is usually not a good electrical conductor . however , as this kind of ribbon is usually relatively thin , typically from 0 . 10 mm to 0 . 40 mm thick , high currents can be conducted provided that the ribbon has sufficient surface area for the overall resistance of the contact strip , i . e . the equivalent resistance between the two series of contacts 3 a and 3 b of all the blades , to remain within acceptable values in terms of heating of the blades by the currents that will flow . if the overall resistance of the contact strip must be reduced without increasing the surface of the ribbon or reducing its thickness , it may be necessary for the metal - plating to be effected on a ribbon that has already been punched , i . e . after the blades have been cut out and possibly twisted and bent . this is because the metal that is a good conductor then covers both surfaces and the edges of each blade . consequently , in a contact strip obtained by this method , the current that flows between the two contacts 3 a and 3 b of a blade is divided between the thickness of the ribbon 9 and the edges of the blade , so that the overall resistance of the contact strip obtained can be reduced to some degree . however , metal - plating at this stage usually entails a significant cost increase compared to an order of operations in which the metal - plating is effected right at the beginning of the process , for the reasons previously stated . the first portion of fig3 is a view of secondary and primary contact strips in longitudinal section in a plane perpendicular to the plane p of the ribbon and passing through its longitudinal axis a . the primary contact strip , obtained after the operation of twisting the blades of the contact strip shown in fig2 can be seen on the right - hand side in fig3 . the blades 3 are spaced by the same original pitch d 1 as the openings 2 . in this representation , the tongues 4 are already inclined relative to the plane p of the ribbon , as can be seen in fig5 . the left - hand side of the figure shows the secondary strip obtained after pleating the two continuous edge strips es 1 and es 2 of the ribbon , so that the blades 3 are spaced by a new pitch d 2 , and before its heat treatment . it must be remembered that in a fabrication method according to the invention the pleating operation mentioned above must take place after metal - plating the ribbon , to avoid poor plating in the mutually overlapping portions of the blades . to give an idea of the orders of magnitude involved , the original pitch d 1 is 2 . 5 mm , for example , and the corresponding new pitch d 2 is 1 . 7 mm , yielding a blade approach factor d 1 / d 2 close to 1 . 5 . it may be noted that the blades partly overlap each other in the direction perpendicular to the plane p of the ribbon . however , the distance between the edge of one blade and the surface of the nearest adjacent blade must remain sufficient for that edge not to come into contact with said surface when the resulting contact strip is installed and compressed between two parts of a connector , such as the two parts 11 and 12 shown in fig5 . accordingly , starting with a given primary contact strip , there is a lower limit for the new pitch d 2 and this limit must not be exceeded . the limit depends in particular on the inclination of the blades to the plane of the ribbon , the required elasticity of the blades , and the width d and the thickness of the blades . it is therefore necessary to arrive at a compromise to obtain a pitch d 2 that is as small as possible , in order to obtain a high blade density combined with a good conduction capacity for high currents . the original pitch d 1 must be sufficient to be able to cut the blades fairly wide so as to be able to bend them and form areas with satisfactory contact surface areas with the two parts of the connector for which it is intended . moreover , it is important to have blades whose width d is sufficient to achieve the required elastic movement in the area of the contacts of each blade , since each blade of the contact strip obtained is able to pivot elastically . however , a wide blade would to some extent make it necessary to increase the new pitch d 2 , which goes against achieving a high density of blades . as it is not desirable for the original pitch d , to be greater than 1 . 25 times the required width d of the blades , as explained in the commentary relating to fig2 it is therefore necessary to arrive at a compromise to minimize the original pitch . there is an optimum range of values for the approach factor d 1 / d 2 , which corresponds to a new pitch d 2 that is sufficiently small to obtain a relatively high blade density from a primary contact strip whose original pitch d 1 is sufficiently large to form blades that are electrically and mechanically satisfactory . a blade approach factor from 1 . 3 to 2 constitutes an optimum compromise and fully satisfies the technical imperatives referred to above . the second portion of fig3 situated under the first portion , is a plan view of the primary and secondary contact strips shown in the first portion of the figure . the mutual overlapping of the blades of the secondary strip is clearly visible on the left - hand side of the figure . after the pleating operation , the tongues 4 are regularly spaced at the same new pitch d 2 as the blades . as can be seen in the first portion of fig3 the pleats 5 formed transversely in the ribbon to move the blades 3 closer together all protrude on the same side of the plane p of the ribbon , preferably the same side as that toward which the tongues 4 are bent . in this way the two continuous edge strips es 1 and es 2 of the ribbon assume a crenelated shape with pairs of crenelations separated by the bottom of a pleat 5 . the internal walls of a pleat 5 do not touch each other , and so there is no risk of the bending applied to the continuous edge strips of the ribbon during pleating breaking the strips . this is most advantageous in the situation in the which the edge strips es 1 and es 2 are covered with a conductive layer 15 like the central strip cs of the ribbon , since it is mainly in the layer 15 that there may be a risk of tearing if the pleats are formed by pressing one wall against another . each pleat therefore has an interior space forming a cavity 6 that is open in the plane p of the ribbon . each cavity has two substantially plane walls that are parallel to each other and perpendicular to the plane of the ribbon in the fig3 embodiment , and also includes a semicylindrical wall that forms the bottom of the cavity 6 . the bottom of this cavity therefore has a curvature diameter δ that corresponds to the diameter of the half - cylinder , and in this embodiment the diameter δ is also equal to the distance between the two plane walls of the cavity . alternatively , it is possible to make pleats 5 with two plane walls that are not parallel to each other , for example of the shape shown in fig3 a . in this figure , one of the two plane walls of the pleat 5 is perpendicular to the plane of the ribbon , but this is not essential and an angle other than 90 ° could equally well be used . the wall that forms the bottom of the cavity 6 partly espouses the shape of a cylinder of diameter δ , and therefore has a curvature diameter equal to δ . each transverse pleat 5 advantageously has a height h such that the ratio d 2 / h between the new regular pitch d 2 and its height is from 1 . 7 to 2 . 5 . the height of a pleat is the distance between the plane surface of the edge strip at the end of the pleat and a plane parallel to that surface which is tangential to the summit of the pleat , assuming that each pleat protrudes from the same side of the plane of the ribbon . for example , the pleat height can be 0 . 85 mm for a new pitch of 1 . 75 mm , which yields a ratio d 2 / h of approximately 2 . the range specified above constitutes a good compromise such that the tongues 4 are sufficiently wide but the pleats 5 are sufficiently high to move the blades 3 closer together with the required new pitch d 2 . the width of a tongue is measured at the level of the longitudinal bend that it forms with a continuous edge strip es 1 , es 2 of the ribbon . the tongues 4 must have some stiffness , combined with some elasticity , first of all so that they can be engaged in grooves in a first part 11 of a connector like that shown in fig5 when fitting the contact strip . the ends of the tongues must then bear sufficiently against the inclined walls of the grooves 13 to hold the contact strip in bearing engagement against the part 11 . if the tongues were too narrow the contact strip would be held against the part 11 insufficiently firmly , and there would be a risk of the strip becoming disengaged when the two parts 11 and 12 of the connector are disconnected . for each transverse pleat 5 satisfying the previously specified range of values for the ratio d 2 / h , the ratio h / δ between the height h of the pleat and the curvature diameter δ of the bottom of the cavity 6 of the pleat is preferably and advantageously from 2 . 4 to 3 . 2 . if the edge strips es 1 and es 2 of the ribbon are covered with a conductive layer 15 , a ratio h / δ in the range specified above in particular allows sufficiently wide bends for there to be no risk of the edge strips breaking during pleating . for example , for a pleat height of 0 . 85 mm , the curvature diameter δ can be 0 . 3 mm , yielding a ratio h / δ of approximately 2 . 8 . [ 0055 ] fig4 is a diagram showing a blade shape slightly different from a more conventional blade shape like that of the contact strip shown in fig2 . the blade 3 has a middle portion 7 that is narrower along the longitudinal axis a of symmetry of the ribbon , as in some prior art embodiments , such as in the patent document ch590570 . this blade shape is appropriate for the middle portion of the blade not to be able to come into contact with a connector part , such as the part 11 or 12 that can be seen in fig5 after the blade is twisted about its axis at and its lateral edges are bent to form the contacts . thus each of the two faces of the blade has two contact areas z 1 and z 2 on respective opposite sides of said middle portion and symmetrical with respect to the axis a . in fig5 a contact strip formed from a ribbon of blades like that shown in fig4 has been installed in a first part 11 of a connector . the contact strip is shown diagrammatically in cross section through a blade in a plane perpendicular to the plane of the ribbon . the first part 11 includes two longitudinal grooves 13 for immobilizing the tongues 4 of the contact strip when the latter has been installed . also , each groove 13 is sufficiently deep for the pleats 5 of the two continuous edge strips es 1 and es 2 of the ribbon not to abut against the bottom of the groove when the contact strip is compressed between the two connector parts 11 and 12 . the first part 11 of the connector has between its two longitudinal grooves 13 a plane or cylindrical longitudinal surface 20 against which the contact 3 b of the bottom face of the blade is pressed and held when the tongues 4 are installed in the grooves . the two end portions 21 and 22 that delimit the longitudinal surface 20 laterally relative to the two longitudinal grooves 13 can constitute edge displacement abutments for the contact strip . in the event of a friction force in the direction transverse to the contact strip , in particular when connecting or disconnecting the two connector parts 11 and 12 , the contact strip tends to move laterally . if the tongues 4 are not sufficiently rigid to limit this movement , the pleats 5 of a continuous edge strip es 1 or es 2 can abut against an end portion 21 or 22 and prevent any further movement . the contact 3 a of the top face of the blade is adapted to bear against a second part 12 of the connector as soon as the two parts 11 and 12 are interconnected . the second part 12 is shown in dashed outline in its connection position . it is clear that each contact 3 a or 3 b consists of two contact areas , such as the areas z 1 and z 2 for the contact 3 a . the surface area of contact between a blade face and a connector part is therefore substantially increased relative to a more conventional embodiment in which each face of a blade has only one contact area . thus the contact resistance between a contact 3 a or 3 b and a respective connector part 12 or 11 can be significantly reduced . [ 0058 ] fig6 shows diagrammatically in cross section part of a contact strip analogous to that shown in fig5 . the connector part that retains the strip includes means for longitudinally immobilizing the strip , which can be advantageous in some relatively marginal embodiments . the means referred to consist of crenelations 14 that correspond to shallower areas of the longitudinal groove 13 , the bottom of a crenelation 14 being formed in this case by the bottom of the groove 13 . once the strip has been fitted , the bosses of the crenelations are closer to the plane p of the ribbon than are the bosses of the pleats 5 . thus if the tongues of the contact strip slide in their retaining grooves 13 if a high force is applied to the contact strip in the longitudinal direction , the pleats 5 abut against the crenelations 14 and prevent further longitudinal movement of the strip . for this kind of embodiment , it is not necessary to have as many crenelations 14 in the grooves 13 as there are pleats 5 in the associated contact strip , as a small number of crenelations distributed over the length of the strip may suffice . [ 0059 ] fig6 a is a diagrammatic view of the device from fig6 in longitudinal section in the plane p ′. as in the device from fig5 the bottom of the groove 13 is sufficiently far away from the pleats 5 not to touch them when the contact strip is compressed . it is clear that the pleats 5 can abut on the sides of the crenelations 14 in the event of longitudinal displacement of the strip . accordingly , with an embodiment as shown in fig6 and 6 a for the first connector part 11 that supports the contact strip , the strip can be nested in this connector part and securely immobilized in the longitudinal direction . this naturally implies immobilizing the strip against rotation if the connector is cylindrical .