referring now to fig1 the numeral 10 indicates generally a bobbin or core made from plastic material , such as polypropylene , formed generally in a frusto - conical configuration , and having a top section or tip end 11 and a bottom section or base end 12 . intermediate tip end 11 and base end 12 , the exterior surface of bobbin 10 has formed thereon a single raised continuous helical thread 13 which , in one embodiment of the present invention , comprises a saw - toothed ridge wrapped in the shape of a helix on the otherwise smooth surface of bobbin 10 as shown in greater detail in fig4 . referring now to fig2 tip end 11 is shown having a dome - shaped top 14 surrounding a central aperture 15 . aperture 15 is better seen in fig3 . as seen in fig2 the relative thickness of the bobbin sidewall 16 at tip end 11 , and the configuration of the dome - shaped top 14 act to reinforce tip end 11 . it should be understood throughout this description of the present invention that , although certain features or embodiments are described as being &# 34 ; formed on &# 34 ; the bobbin , the bobbin is , in its preferred form , injection - molded as a unitary structure , and all of the structure so described is integral with the bobbin . in other words , in its preferred form , the bobbin is a one - piece construction , rather than a substrate with various surface details added thereto such as by adhesives or fasteners . as best seen in fig2 and 3 , a preferred embodiment of the present invention has a series of longitudinally or axially extending skeletal ribs formed on the interior of bobbin 10 . in fig2 one embodiment of the present invention includes a number of full ribs 18 which extend from tip end 11 to a point proximate base end 12 . in fig3 the construction illustrated utilizes a series of six such full ribs equally spaced about the interior surface of bobbin 10 . also illustrated in fig2 is a series of circumferentially extending skeletal , or circular ribs , 19 , 20 , and 21 . ribs 19 , 21 , and 21 are formed concentrically along the axis of bobbin 10 , and intersect full ribs 18 at , for example , junctures 22 , 23 and 24 of fig2 . the embodiment depicted in fig2 also includes a series of shortened or partial longitudinally extending ribs exemplified by the numerals 25 , 26 , 27 and 28 . generally , each such partial rib , when viewed within bobbin 10 , appears thickest where it intersects a circular rib , and thereafter appears to blend in with the inner surface bobbin 10 . the nature and character of the construction of such partial ribs will be more extensively developed hereinafter , when further details of the sidewall construction of bobbin 10 are discussed . referring now to fig2 and 4 , and , more particularly , to the details of construction of the sidewalls of bobbin 10 , it can be seen that at various points along the length of bobbin 10 , the thickness of the sidewall 16 varies . in the embodiment shown in fig2 longitudinal segments of cone 10 have been divided , for purposes of illustration into segments a , b , c , and d , and a partial side sectional view representative of one such section is shown in fig4 . the segment in fig4 extends from a first circular rib 30 downward to a second circular rib 31 , as a typical section . as seen in fig4 the exterior surface 32 of sidewall 16 is formed with a constant taper relative to the axis of bobbin 10 , as illustrated by line e . one such taper utilized in such bobbins is 5 ° 57 &# 39 ; as measured by a line coextensive with the outer bobbin wall intersecting the axis of the bobbin . as typified by line f , an interior surface segment 33 of sidewall 16 is formed with a taper which differs from that of exterior surface 32 . the result of such a taper is to create a wall section with segments of varying thickness . one such taper ( measured in the same fashion as the true taper ), found to be effective is approximately 5 ° 54 &# 39 ;. the embodiment in fig4 is characterized by a sidewall construction at which the wall is at its thickest at 35 , that is , at its juncture with the upper part of circular rib 31 , and which thereafter tapers to narrow until it reaches point 36 , and thereafter continues at a uniform thickness until it meets circular rib 30 . another such construction may have the taper continue from circular rib 31 where it meets circular rib 30 . as seen in fig4 the next upper most wall section 37 begins with a thickened segment at the top of circular rib 30 , while the next subjacent wall section 38 terminates with a narrowed portion at circular rib 31 . in this fashion , less plastic material is required to manufacture each bobbin 10 while the arrangement of full and partial longitudinal ribs , and circular ribs , provides the bobbin construction with the strength to resist the compressive and centrifugal forces described hereinabove , encountered when bobbin 10 is placed upon a spinning mandrel and used to wind yarn . as seen in fig4 partial rib 39 is actually of substantially constant thickness , and follows the taper of the inner wall segment . the lower end of rib 39 blends in with sidewall 16 as at 40 , when the thickness of the sidewall matches the maximum thickness of sidewall 16 . thus , with respect to the partial ribs , at least a portion of each such rib is equal to or less than thickness of one portion of sidewall 16 . with respect to longitudinal rib 18 , said rib is formed with a thickness which equals the maximum thickness of wall section 16 , and is formed with the same inner taper as the outer taper of sidewall 16 of bobbin 10 . a preferred embodiment of the circular ribs shown at , for example , 30 and 31 of fig4 has each such circular rib formed with a constant thickness . thus , in one version of the present invention , bobbin 10 has a first section a within which the wall thickness tapers upward from base end 12 to first circular rib 21 , a second section b with a thickened base tapering upward to circular rib 20 , a third section c with a wall section tapering upward to circular rib 19 and a fourth section d with a wall section which tapers upward to tip end 11 . referring now to fig1 and 4 , the numeral 41 indicates generally the raised , helically formed saw - tooth thread formed about the circumference of bobbin 10 . as seen in fig4 said threads 41 are formed with sharp , downwardly - facing edges 45 which enables the surface of cone 10 to more effectively snag a yarn segment to initiate the winding operation , yet which allows for easy removal of the finished bobbin from its mold . in yet another preferred embodiment , illustrated in fig5 bobbin 10 has internally - formed surface grooves 42 about a section of the inner periphery of bobbin 10 proximate base end 12 . the grooves so formed provide a gripping segment which enhances the holding of bobbin 10 on the mandrel of an automatic winding apparatus . preferably , grooves 42 are formed to be contiguous with a circular rib such as 43 , and a series of shortened partial ribs 44 may also be formed in order to reinforce the base end 12 of bobbin 10 . grooves 42 also provide advantages in separating bobbins which are shipped nested one within the other , and in removing bobbin 10 from a mandrel once winding is complete . grooves 42 , and full ribs such as 18 , form a bearing surface for a mandrel . at least three such ribs 18 , formed with a true taper and constant thickness , equal to or exceeding the maximum wall thickness of bobbin 10 , are spaced equidistantly about the inner periphery of bobbin 10 . a preferred version of bobbin 10 utilizes six such full or true taper ribs alternating with axially - spaced files of partial ribs . full ribs 18 should be spaced uniformly about the interior of bobbin 10 such that each full rib is the same distance from its preceding and following full ribs , i . e ., three full ribs would be placed at 120 ° intervals , four full ribs at 90 ° intervals , five full ribs at 72 ° intervals , six full ribs at 60 ° intervals , etc . as seen in fig5 use of partial ribs 29 and 44 can represent a greater saving of raw material , where no such ribs hereto exceeds the thickness of sidewall 16 throughout the entire length of bobbin 10 . in one such version of bobbin 10 , use of partial ribs and varying wall thicknesses enabled the saving of 21 / 2 pounds of polypropylene per 1 , 000 bobbins . placement of circular ribs such as 29 , 30 and 31 may vary with the size and exterior taper of bobbin 10 . as seen in fig5 circular rib 43 and grooved section 42 combine to reinforce base end 12 . while the foregoing has described certain specific embodiments of the present invention , it is to be understood that these embodiments are being presented by way of example only . it is expected that others skilled in the art will perceive variations which , while differing from the foregoing , do not depart from the spirit and scope of the invention as herein described and claimed .