those shown in fig7 in this configuration teeth 50 and 52 are equally rounded on their upper and lower corners as you approach the sine wave form with the fig9 configuration the increase in center to center distance of the gears greatly increases the side clearance distance faster than the involute form thereby reducing the desired flattening of the fibers as with the fig7 tooth shape the stretching rollers 18 and 20 fig3 in this particular example each have four sets of meshed parallel helical teeth 54 through 60 and 62 through 70 which are disposed in a herringbone pattern in which the teeth of each set of teeth are inclined at an angle to the ends of the roller and to the teeth of adjacent sets in each set of teeth 54 through 70 the individual teeth of the set are helical in form and are each disposed at a helix angle a to the end of the corresponding roller and are disposed at an angle b to the teeth of the adjacent set angle b is equal to twice angle a the angle a may be any desired acute angle and is chosen by consideration of the desired ratio between the elongation of the web 10 in the longitudinal dimension and its elongation in the lateral dimension when the angle a equals 45 u00b0 the longitudinal elongation of web 10 is approximately equal to the lateral elongation thereof when the angle a is greater than 45 u00b0 the longitudinal elongation of web 10 exceeds the lateral elongation thereof when the angle a is less than 45 u00b0 the lateral elongation of web 10 exceeds the longitudinal elongation thereof the lateral elongation is approximately equal to the.