extends in a helix surrounding the roller body the working width of the roller is approximately 2 m the distance between adjacent turns of the helix i e the axial distance from one rib peak to the next is about 15 mm resulting in a total of about 130 rib peaks along the roller length thus fig2 and 3 are not shown to scale the rollers 1 and 2 of fig2 are of similar form having complementary reliefs formed in their periphery with the helical turns of the reliefs 34 engaging 34 as shown in fig2 the rollers 1 2 are designed to rotate relative to one another at the same speed without the flanks of the helical relief 15 coming into engagement thus while reference may be made to the reliefs or the rollers engaging it should be appreciated that there is no actual contact there is instead meshing of the reliefs during rotation of the rollers 1 2 the width extending nip 12 retains its corrugated shape and uniform width fig3 shows an alternative embodiment of a helical relief 15 39 each cylindrical roller 1 2 has helical turns extending outwards from a centre plane 16 which is perpendicular to the roller axis the pitch to peak height s i e the difference in radius between peaks 17 and troughs 18 of the helix is constant on both sides of the plane 16 but the pitch on the two sides has opposite signs that is to say the helical relief 15 39 starting from the centre plane 16 has a right hand thread on one side and a.