in fig1 a boot 1 is shown attached by straps 2 to an outer - sole 3 . the outer sole 3 has metal studs 4 attached to posts 5 descending from the lower tread element 6 of the outer sole . an upper sole element 7 lies bonded to the tread element 6 , suitably by glue , sonic welding or the equivalent . upwardly - curled toe 8 and heal 9 portions regions of the outer - sole 3 lie in contact with the toe 10 and heel 11 portions of the boot , pressing preferentially into such portions . in fig2 the tread element 6 of the outer - sole 3 is shown to have transverse ridges 12 which are , in this example , chevron - shaped . any other shapes adapted to provide traction on soft - soil will be suitable , the chevron format being known to release mud and snow readily . such ridges 12 are separated by inter - ridge gaps 13 that extend across the entire width of the outer - soles 3 and allow the outer - sole 3 to flex . posts 5 carry metal studs 4 which may conveniently be self - tapping metal screws . the height of each post 5 is substantially the same as the maximum height of the most proximate ridge 12 . in fig3 the upper sole 7 and lower tread 6 elements of the outer - sole 3 are shown before assembly . the upper sole element 7 may be made of a thin rubber sheet or equivalent , textured on its upper surface 13 to better engage the lower sole surface of the boot 1 . the upper sole element 7 , which may be of 3 mm thickness , is shown as being slightly shorter than the lower tread element 6 . this is to allow for stretching during the manufacturing process . on a sole of overall length of 23 cm , it has been found satisfactory for the upper sole element 7 to be shortened by about 1 / 2 cm at each end . in assembling the upper and lower sole and tread elements 7 , 6 , together , the central region 14 of the sole element 7 is first bonded to the tread element 6 , conveniently by contact cement . on a 23 cm sole this central region 14 may extend over 10 - 14 cm . after this initial bonding has set , the upper sole element 7 is stretched in its toe and heel regions and then glued , as by contact cement , to the toe and heel regions 8 , 9 of the outer sole 3 . this causes the toe and heel regions 8 , 9 of the outer sole 3 to curl upwards , and this configuration is allowed to remain until the bonding sets . the upper and lower sole and tread elements 7 , 6 are then stitched together by stitching 15 , around their outer margins . as can be seen in fig1 the effect of the curled portions is to press the toe and heel regions 8 , 9 of the outer sole 3 against the lower sole of the boot 1 , in the vicinity of its toe and heel portions 10 , 11 of the boot 1 . it has been found that the combined strengths of the materials and degree of stretching in the upper sole element 6 should produce an up - turn , at the toe and heel regions of the outer sole 3 , to an angle of about 55 degrees ± 5 degrees . the foregoing has constituted a description of specific embodiments showing how the invention may be applied and put into use . these embodiments are only exemplary , the invention in its broadest , and more specific aspects , is further described and defined in the claims which now follow .
an outer - sole to be worn over footwear is characterized by having a curled forward or toe portion , and optionally heel portion as well , that holds the front portion of the outer - sole in contact with the footwear to which it is attached .