this end plate presents an outer edge 11 a that comprises in succession a first cylindrical portion 12 a joining the plane outer face 7 a extended by a bearing face 13 a in the shape of a plane circular annulus and itself extended by a second cylindrical portion 14 a joining the plane inner face 8 a the second end plate 4 b has the same shape as the first end plate 4 a and likewise comprises an outer face and an inner face 7 b and 8 b that are plane together with a central orifice 9 b its edge 11 b is likewise constituted by three portions 12 b to 14 b identical to the portions 12 a to 14 a as can be seen in the figures the first cylindrical portions 12 a and 12 b are of a diameter that corresponds to the outside diameter of the pin 1 the second cylindrical portions 14 a and 14 b have a smaller diameter that corresponds to the diameter of the inside face 5 of the pin 1 for the purpose of centering each of the end plates in the corresponding end of the pin 1 these end plates are thus generally axially symmetrical in shape and they present thickness that is small being of the order of a few millimeters in addition at least one of the end plates includes one.