surface 9 and secondly with the outer surface of the mixing roller 12 with which it comes into contact thus the association of the choice of hardness of the wheel and the form of the circumferential surface 9 enables the surface 8 to fit both the sizing cylindrical revolution surface of the roller 12 and the non cylindrical groove bottom surface 8 in the embodiment described above the flexible extended or elongated element 1 comprises two lateral plane surfaces 7 perpendicular to the groove bottom surface 9 and the sizing wheel 2 includes two plane ring shaped surfaces 6 it is also within the scope of this invention to use it when at least one of the plane lateral surfaces 7 is not perpendicular to the axis of the sizing wheel 2 and when it could cooperate at least with one outer circumference of a ring shaped surface 6 either without deformation of the sizing wheel 2 and or the flexible extended or elongated element 1 or with deformation of one and or the other especially when they are elastic thus the plane lateral surfaces 7 of the extended or elongated element 1 might tend to close or open the extended or elongated element 1 thus the lateral surfaces of the element might tend to close the element or open it similarly the ring shaped surface s 6 need not necessarily be planar and could be truncated the top of the cone on which rests the ring shaped surface 6 which is the axis 5 of the.