Abstract:
A one-piece bi-directional cable tie for bundling articles having a tail at one end, a locking head at the other end and an elongate strap body therebetween may feature one or more fixed locking teeth opposite a deflectable locking pawl so as to provide ratcheting locking engagement with the two major surfaces of its strap body. The fixed teeth may provide symmetrical performance characteristics or may provide selectable performance characteristics depending on the direction of strap body insertion through the locking head. The locking head may facilitate wedging the strap body against the deflectable pawl. The deflectable pawl may include a chevron-shaped upper surface so as to provide an undercut surface for improved engagement with the locking teeth of the strap body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/066,123, filed Nov. 21, 1997 and to U.S. Provisional Patent Application Ser. No. 60/077,514, filed Mar. 11, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a self-locking cable tie for securing a plurality of wires or similar articles. More particularly, the present invention relates to a bi-directional cable tie which allows strap insertion though the head in either direction. 
     BACKGROUND OF THE INVENTION 
     The use of cable ties to bundle a plurality of wires or similar articles has long been known. Basic cable tie construction includes an elongate cable tie strap having a tail at one end and a head at the other end. The head includes a central passage or aperture therethrough for accommodating a tail in an insertable fashion. The head supports a locking device adjacent the head aperture to securely lock the cable tie body within the aperture of the head to provide securement of the cable tie about the bundle of wires. In one type of cable tie construction, the locking device is a flexibly supported integrally formed pawl having plastic teeth which engage corresponding teeth on a cable tie body to provide locking engagement therebetween. As is typical of most cable ties, the tail of the cable tie is inserted into the head aperture uniquely in one direction. However, the art has also seen the use of bi-directional, or symmetrically-formed, cable ties which permit the cable tie tail to be inserted through the aperture in the head in either direction. 
     One such bi-directional cable tie is shown and described in co-pending commonly assigned U.S. application Ser. No. 08/689,466, filed Aug. 9, 1996, entitled “A Self-Locking Cable Tie Strap With Symmetrical Structure”, issued on Mar. 23,1999, as U.S. Pat. No. 5,884,367 which is herein incorporated by reference for all purposes. The cable tie of such construction may be particularly used with an automatic cable tie installing device where a plurality of cable ties held together in a reel. A cable tie from the reel may be fed from a dispenser to a cable tie installing gun for installation about a plurality of wires. The symmetrical construction of the cable tie permits the cable tie to be easily dispensed and aligned within the installation gun. As may be appreciated, in order to accommodate insertion of the cable tie tail from either direction, the pawl or locking device of the symmetrical cable tie must be sufficiently flexible to permit deflection in either direction. Such flexibility assures that the cable tie tail may be easily inserted through the aperture in the head in either direction. 
     While such flexible construction permits easy insertion, it has been found that in certain circumstances such cable ties may not exhibit sufficiently high resistance to withdrawal forces as may be required in certain applications. Additionally, the art has uniformly provided bi-directional cable ties having symmetrical withdrawal-resistance characteristics while ignoring circumstances where it may be desirable to provide a bi-directional cable tie exhibiting discretely selectable, or non-symmetrical, withdrawal-resistance characteristics depending upon which direction the cable tie strap is inserted through the head. 
     Accordingly, it is desirable to provide a cable tie having a self-locking feature in a symmetrical structure which exhibits ease of insertion of the cable tie strap into the aperture in either direction and yet provides suitably high resistance to withdrawal forces in order to maintain a self-locking configuration. Additionally, it is desirable to provide a self-locking feature in an asymmetrical structure which offers discretely-selectable resistance to withdrawal forces according to the direction of strap insertion. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a bi-directional cable tie for bundling one or more articles. 
     It is another object of the invention to provide a bi-directional cable tie having improved performance characteristics. 
     It is still another object of the invention to provide a bi-directional cable tie having a fixed locking teeth capable of engaging the teeth on the other side of the strap body as those engaging the locking pawl. 
     It is yet another object of the present invention to provide a bi-directional cable tie providing asymmetric performance characteristics in that the hoop strength depends on the direction through which the strap body is inserted into the passageway. 
     It is even yet another object of the present invention to provide a bi-directional cable tie with the locking teeth of the locking pawl include an undercut strap engaging surface so as to increase the range of pawl deflection providing locking engagement between the pawl and the strap body. 
     In the efficient attainment of these and still other objects, the present invention provides a bi-directional cable tie for bundling one or more articles having a locking head at one end, a tail at the other end and an elongate strap body therebetween. The strap body includes opposing first and second major surfaces having a plurality of locking teeth formed on each major surface. The locking head includes a first opening, a second opening, and an elongate strap passageway extending therebetween in a direction substantially perpendicular to the strap body. The head also provides opposed shoulder and block surfaces extending along the passageway. The shoulder surface provides a first rotation stop surface adjacent the first opening and a second rotation stop surface adjacent the second opening. A deflectable locking pawl extends from the shoulder surface into the passageway across from the block surface. The locking pawl is substantially aligned with the strap body and is deflectable by the strap body upon insertion of the strap body in either direction through the passageway. The locking pawl also provides locking engagement with the strap body upon attempted withdrawal of the strap body in a direction opposite to the insertion direction. The locking pawl includes a locking portion having a first locking tooth facing both the first opening and the passageway and a second locking tooth facing both the second opening and the passageway, and an elongate pawl base including a first cantilever arm having a first free end extending towards the first opening and a second cantilever arm having a second free end extending towards the second opening. The pawl base is connected to the shoulder by a flexible hinge which defines the closed end of both a first notch bounded by the first cantilever arm and the first stop surface and opening towards the first opening of the head, and a second notch bounded by the second cantilever arm and the second stop surface and opening towards the second opening of the head. When the strap body is inserted through one end of the passageway it contacts the near locking tooth of the locking pawl and causes the locking pawl to translate and rotate about the flexible hinge towards the opposite end of the passageway so that the free end of the oppositely-extending cantilever arm engages its opposing rotation stop so as to close the notch opening towards the exit end of the passageway. Attempted withdrawal of the strap body back through the passageway causes the contacted locking tooth of the pawl to engage a locking tooth of the strap body and counter-rotate the locking pawl about the hinge to thereby force the strap body against the block surface of the head; and 
     The present invention also contemplates increasing the hoop strength of the cable tie of the present invention by providing one or more fixed locking teeth on the block surface of the cable tie head for engaging the locking teeth on the opposite surface of the strap as those engaging the deflectable pawl. In one embodiment of the present invention a fixed locking tooth is provided adjacent each opening so as to engage the strap upon withdrawal back through the adjacent opening. The fixed locking teeth are symmetrically provided so as to offer substantially the same performance characteristic regardless of the insertion direction of the strap body through the passageway in the head. 
     In another embodiment of the present invention a fixed locking tooth is provided to effectively resist withdrawal through in only one direction. This asymmetric bi-directional cable tie therefore offers a discretely-selectable performance characteristics depending upon the direction in which the strap body is inserted through the passageway. That is, the hoop strength will be higher when the strap body is inserted into the passageway in the direction that provides locking engagement between the fixed tooth and the strap body than when inserted through the passageway in the other direction. 
     In yet another embodiment of present invention the first and second rotation stop surfaces of the shoulder are formed having a pronounced taper so as to face both the adjacent opening in the cable tie head and the passageway. The tapered stop surfaces provide a wedge surface enabling the opposed cantilever arm to slide towards the hinge to thereby further pin the strap body against the block surface of the head. 
     In even still another embodiment of the present invention, the locking pawl provides a chevron-shaped upper surface in facing opposition to the block surface so that the first and second locking teeth of the pawl provide improved locking engagement with the teeth of the strap body. The chevron-shaped upper surface is desirably formed by the side-by-side formation of a pair of locking teeth having a first surface facing the closest opening in the head and a second surface facing both the passageway and the other opening of the head. 
     The present invention will be more readily appreciated in a reading of the “Detailed Description of the Invention” with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a top elevational view of a cable tie of the present invention. 
     FIG. 2 shows a side elevational view of the cable tie of FIG.  1 . 
     FIG. 3 shows a longitudinal cross-sectional view of the cable tie of FIG. 1 taken through the line  3 — 3 . 
     FIG. 4 is a cross-sectional view detailing the deflectable pawl of the cable tie of FIG.  1 . 
     FIG. 5 is a partial cut-away view of the cable tie of FIG. 1 in an assembled configuration. 
     FIG. 6 is a top elevational view of an alternate embodiment of the cable tie of the present invention. 
     FIG. 7 is a longitudinal cross-sectional view of the cable tie of FIG.  6 . 
     FIG. 8 is a cross-sectional view detailing the deflectable pawl of the cable tie of FIG.  6 . 
     FIG. 9 is a partial cut-away view of the cable tie of FIG. 6 in an assembled configuration. 
     FIG. 10 is a partial cut-away view of an alternate embodiment of the cable tie of FIG. 6 in which the head include a single fixed locking tooth in facing opposition to the pawl. 
     FIG. 11 is a front elevational view of an alternate embodiment of the cable tie head and deflectable pawl of the cable tie of the present invention. 
     FIG. 12 is a cross-sectional view of the cable tie head and deflectable pawl taken through the line  12 — 12  in FIG.  11 . 
     FIG. 13 is a cross-sectional view of the passageway through the cable tie head taken though the line  13 — 13  in FIG.  11 . 
     FIG. 14 is a perspective cross-sectional view of the cable tie head taken through line  14 — 14  in FIG.  11 . 
     FIG. 15 is a cross-sectional view of the cable tie head of FIG. 11 in an assembled configuration. 
     FIG. 16 is a cross-sectional view of still another embodiment of the cable tie of the present invention providing undercut strap engaging surfaces on the locking teeth of the deflectable pawl. 
     FIG. 17 is a cross-sectional view detailing the deflectable pawl of the cable tie of FIG.  16 . 
     FIG. 18 is a front elevational view of the locking pawl of the cable tie of FIG.  16 . 
     FIG. 19 is a perspective cross-sectional view of the head of the cable tie of FIG. 16 detailing the locking teeth of the deflectable pawl. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-3, a cable tie  10  of the present invention is shown. Cable tie  10  is of the type referred to as a bi-directional cable tie. Cable tie  10  is generally integrally formed of a suitable molded plastic such as nylon. 
     Cable tie  10  includes an elongate cable tie strap body  12  terminating at one end in a cable tie tail  14  at the other end and a cable tie head  16 . Cable tie strap body  12  is generally a planar member having a plurality of notches or teeth  18  extending along each of opposed planar surfaces  18   a  and  18   b  thereof. As will described in further detail hereinbelow, teeth  18  on each surface  18   a  and  18   b  are staggered with respect to one another. Thus, the raised ridges  40  of teeth  18  on surface  18   a  are non-aligned with the raised ridges of  40  of teeth  18  on surface  18   b . By staggering the teeth in such a manner, the respective depressions  42  between teeth are not aligned. This avoids the cable tie strap body having a thinned or narrowed cross-sectional thicknesses along the length thereof. Such a construction improves the radial hoop strength of the cable tie in use and reduces incidences of failure from breakage. 
     Cable tie head  16  defines a first aperture  17 , a second aperture  19 , and an elongate passageway  20  extending therebetween for insertably accommodating the cable tie tail  14  therethrough. As shown in FIG. 5, cable tie tail  14  is inserted generally in the direction of arrow A, however it may be appreciated due to the symmetrical configuration of cable tie  10 , cable tie tail  14  may also be inserted in the direction opposite arrow A. 
     With additional reference to FIGS. 4 and 5, cable tie head  16  includes a shoulder  25  and a block surface  21  extending along passageway  20  in facing opposition. Head  16  further includes an integrally-formed pawl  22  extending into aperture  20 . Pawl  22  is a symmetrical structure extending from a central hinge  24  integrally formed with strap body  12 . Pawl  22  includes a locking element  26  and an elongate pawl base  48  which are symmetrically constructed having a pair of pawl teeth  50 ,  52  and cantilever arms  54 ,  56  on each side thereof. First pawl tooth  50  includes first and second pawl tooth surfaces  50   a ,  50   b  facing first aperture  17  and block surface  21 , respectively. Similarly, second pawl tooth  52  includes first and second pawl tooth surfaces  52   a ,  52   b  facing second aperture  19  and block surface  21 , respectively. Cantilever arm  54  extends towards first aperture  17  and terminates at a first free end  54   a . Cantilever arm  56  extends towards second aperture  19  and terminates at a second free end  56   a.    
     Hinge  24  is positioned on and extends from a shoulder  25  of strap body  12 . Hinge  24  defines the closed ends of a first notch  60 , opening towards first aperture  17 , and a second notch  62 , opening towards second aperture  19 . Shoulder  25  forms a first rotation-stop surface  25   a  across first notch  60  from cantilever arm  54  and a second rotation-stop surface  25   b  across second notch  62  from second cantilever arm  56 . Stop surfaces  25   a  and  25   b  limit the rotation of pawl  22  due to strap insertion through passageway  20 , thereby maintaining pawl  22  in ratchet engagement with strap body teeth  18 . Cantilever arms  54 ,  56  are designed so that upon rotation of locking element  26 , the free end  54   a ,  56   a  of the arm  54 ,  56  not engaging the strap body  12  extends over and against its underlying rotation stop surface  25   a ,  25   b  to thereby close its respective notch  60 , 62 . Such construction permits the strap body  12  to be easily inserted through aperture  20 . 
     For example, upon insertion of cable tie tail  14  into aperture  17 , pawl tooth  50  and cantilever arm  54  engage strap body teeth  18  on one planar surface  18   a  of strap body  12 . Locking element  26  is deflectable about hinge  24  to permit continued insertion of strap body  12  through passageway  20 . Pawl tooth  50  and cantilever arm  54  are each engageable with strap body teeth  18  on surface  18   a  so as to provide ratcheting interlocking engagement therewith. Such ratcheting interlocking engagement permits the strap to be continually inserted in the direction of arrow A yet prevents withdrawal of strap body  12  from head  16  in the direction opposite arrow A. Upon attempted withdrawal, pawl tooth  50  and cantilever arm  54  urge strap body  12  against upper wall  21  due to the counter rotation and translation of pawl  22  about and across hinge  24  and stop surface  25   b.    
     A further improvement in the cable tie of the present invention is shown in FIGS. 4 and 5. Cable tie  10  further includes a modification to the upper wall  21 . In the present illustrative embodiment upper wall  21  includes inwardly tapered entry surfaces  31  adjacent apertures  17  and  19  of head  16 . Tapered surfaces  31  facilitate ease of insertion of cable tie tail  14  into passageway  20 . Furthermore, upper wall  21  includes a centrally disposed inwardly directed wall portion  32  extending towards pawl  22 . Wall portion  32  is an elongate member which projects downwardly from wall  21  to reduce the opening within passageway  20 . This assures engagement between ratchet teeth  18  of strap body  12  and locking element  26  upon insertion of strap body  12  into passageway  20 . 
     In addition, wall portion  32  further includes at each end thereof, a tapered projection  35  which extends further downwardly into passageway  20 . Projections  35  straddle each side of pawl  22 . Upon insertion of strap body  12  into passageway  20 , the teeth  18  on surface  18   a  are engageable with the projection  35   a  positioned adjacent the exit end of passageway  20 . Deflection of pawl  22  permits continued insertion of strap body  12  in the direction of arrow A. Upon an attempt to withdraw strap body  12  in a direction opposite arrow A, teeth  18  on surface  18   a  become interlocked with projection  35   a  further preventing withdrawal of strap body  12  from passageway  20 . As may be appreciated, projection  35   b  operates in the same manner when tail  14  is inserted into passageway  20  in a direction opposite arrow A. 
     Such construction of head  16  as is shown herein results in a cable tie  10  being resistant to higher withdrawal forces without significantly increasing the force required to insert the tail into passageway  20 . 
     Referring now to FIGS. 6-9, cable tie  110 , an alternate embodiment of the present invention, is shown. Similar numbering relates to similar components previously described. Cable tie  110  is a bi-directional cable tie having improved features which provide for enhanced resistance to withdrawal forces in one direction. The operation of pawl  122  and its locking engagement with strap body  112  is generally as previously described. Cable tie  110  is generally integrally formed of a suitable molded plastic such as nylon. Cable tie  110  includes an elongate cable tie strap body  112  including at one end a cable tie tail  114  and at the other end at a cable tie head  116 . 
     Cable tie  110  includes an elongate cable tie strap body  112  terminating at one end in a cable tie tail  114  at the other end and a cable tie head  116 . Cable tie strap body  112  is generally planar having a plurality of notches or teeth  118  extending in staggered relationship along each opposed planar surface  118   a  and  118   b  thereof. Cable tie head  116  defines a first aperture  117 , a second aperture  119 , and an elongate passageway  120  extending therebetween for insertably accommodating the cable tie tail  114  therethrough. As shown in FIG. 9, cable tie tail  114  is inserted generally in the direction of arrow A, however it may be appreciated due to the symmetrical configuration of cable tie  110 , cable tie tail  114  may also be inserted in the direction opposite arrow A. 
     With additional reference to FIGS. 7 and 8, cable tie head  116  includes a shoulder  125  and a block surface  121  extending along passageway  120  in facing opposition. Head  116  further includes an integrally-formed pawl  122  extending into passageway  120 . Pawl  122  is a symmetrical structure extending from a central hinge  124  integrally formed with strap body  112 . Pawl  122  includes a locking element  126  and an elongate pawl base  148  which are symmetrically constructed having a pair of pawl teeth  150 ,  152  and cantilever arms  154 ,  156  on each side thereof. First pawl tooth  150  includes first and second pawl tooth surfaces  150   a ,  150   b  facing first aperture  117  and block surface  121 , respectively. Similarly, second pawl tooth  152  includes first and second pawl tooth surfaces  152   a ,  152   b  facing second aperture  119  and block surface  121 , respectively. While first and second pawl teeth  150  and  152  are shown having a dissimilar size and shape, it is contemplated that need they may similarly formed as shown for cable tie  10 . Cantilever arm  154  extends towards first aperture  117  and terminates at a first free end  514   a . Cantilever arm  156  extends towards second aperture  119  and terminates at a second free end  156   a.    
     Hinge  124  is positioned on and extends from a shoulder  125  of strap body  112 . Hinge  124  defines the closed ends of a first notch  160 , opening towards first aperture  117 , and a second notch  162 , opening towards second aperture  119 . Shoulder  125  forms a first rotation-stop surface  125   a  across first notch  160  from cantilever arm  154  and a second rotation-stop surface  125   b  across second notch  162  from second cantilever arm  156 . Stop surfaces  125   a  and  125   b  limit the rotation of pawl  122  due to strap insertion through passageway  120 , thereby maintaining pawl  122  in ratchet engagement with strap body teeth  118 . Cantilever arms  154 ,  156  are designed so that upon rotation of locking element  126 , the free end  154   a ,  156   a  of the arm  154 ,  156  not engaging the strap body  112  extends over and against its opposite rotation stop surface  125   a ,  125   b  to thereby close its respective notch  160 ,  162 . Such construction permits the strap body  112  to be easily inserted through passageway  120 . 
     In order to improve the locking capability of the cable tie of the present invention and in order to enhance the prevention of withdrawal of the strap body in a direction opposite the direction of insertion, the present invention configures upper wall  121  as shown in FIGS. 6-9. Upper wall  121  includes a non-symmetrical surface  130  having a pair of generally ramped or angled surfaces  131  and  133  which extend into passageway  120  and are asymmetrical to one side of the aperture. The end of ramped surfaces  131  and  133  forms spaced apart ledges  132  and  134  which define locking notches for engagement with the teeth of strap body  112 . 
     As particularly shown in FIG. 9, strap body  112  may be inserted in the direction of arrow A. The dual tapered or ramped configuration of surface  130  helps guide strap body  112  through passageway  120  in such a direction. Upon such insertion of strap body  112  into passageway  120 , pawl  122  is deflected. Continued insertion of strap body  112  into passageway  120  is permitted by the particular configuration of ramped surface  131 . Upon an attempt to withdraw strap body  112  from passageway  120  in a direction opposite arrow A, locking element  126  engages strap body teeth  118  on surface  118   b  in a manner described hereinabove. However, the particular configuration of surface  130  further resists the withdrawal forces as ledges  132  and  134  also engage successive ridges  140  of teeth  118  on the opposed surface  118   a  of strap body  112 . The distance which ledges  132  and  134  are spaced apart on surface  130  is approximately equivalent to the pitch or spacing between teeth  118  on surface  118   a  of strap body  112 . Such dual locking capability on both sides of strap body  112  helps retain strap  112  in a locked configuration within passageway  120  against withdrawal forces. Thus, the cable tie shown in FIG. 8 is particularly resistant to withdrawal forces applied in a direction opposite arrow A of the insertion direction. 
     However, it may be appreciated that while the particular construction shown herein allows easy insertion of the strap body into passageway  120  in the direction of arrow A and prevents withdrawal of the strap body in the direction opposite arrow A due in part to the improved configuration of surface  130 , the cable tie shown herein may be used in conventional symmetrical fashion, i.e., the cable tie may still be employed with the insertion direction being the direction opposite arrow A and a withdrawal direction being in the direction of arrow A. Thus, the present invention while providing a symmetrical structure where the body may be locked in the head aperture in either direction provides superior performance characteristics when used in a manner shown in FIG.  9 . 
     Referring to FIG. 10, cable tie  110 ′ is shown. Cable tie  110 ′ substantially similar to cable tie  110  shown in FIG. 7 with each element being substantially identical and operating in a substantially identical manner. However, cable tie  110 ′ includes a further embodiment of upper wall  121 ′ wherein surface  130 ′ includes a single ramped surface  134 ′ extending into and towards one side of passageway  120 ′. The ramped surface  134 ′ forms a downwardly extending ledge  137 ′ within passageway  120 . Thus, upon an attempt to withdraw strap body  112 ′ from passageway  120 ′ ledge  137 ′ engages one of the ridges  140 ′ of teeth  118 ′ on surface  118   a ′ so as to provide further redundant locking engagement therewith. As with the embodiment described above, the present embodiment, enhances the resistance to withdrawal forces of the cable tie where the strap body is attempted to be withdrawn in a direction opposite arrow A. However, as with the embodiment shown in FIG. 6, the cable tie  110 ′ functions in a symmetrical manner by allowing strap body  112  to be inserted in head aperture in either direction. 
     Referring now to FIGS. 11-15, cable tie  210 , a further embodiment of the present invention, is shown. Similar numbering relates to similar components previously described. Cable tie  210  is a bi-directional cable tie having features which provide for enhanced resistance to withdrawal forces by facilitating the pawl wedging the strap body against the block surface. The operation of pawl  222  and its locking engagement with strap body  212  is generally as previously described. Cable tie  210  is generally integrally formed of a suitable molded plastic such as nylon. 
     Cable tie  210  includes an elongate cable tie strap body  212  terminating at one end in a cable tie tail  214  at the other end and a cable tie head  216 . Cable tie strap body  212  is generally planar having a plurality of notches or teeth  218  extending in staggered relationship along each opposed planar surface  218   a  and  218   b  thereof. Cable tie head  216  defines a first aperture  217 , a second aperture  219 , and an elongate passageway  220  extending therebetween for insertably accommodating the cable tie tail  214  therethrough. As shown in FIG. 15, cable tie tail  214  is inserted generally in the direction of arrow A, however it may be appreciated due to the symmetrical configuration of cable tie  210 , cable tie tail  214  may also be inserted in the direction opposite arrow A. 
     With additional reference to FIGS. 12 and 15, cable tie head  216  includes a shoulder  225  and a block surface  221  extending along passageway  220  in facing opposition. Head  216  further includes an integrally-formed pawl  222  extending into passageway  220 . Pawl  222  is a symmetrical structure extending from a central hinge  224  integrally formed with strap body  212 . Pawl  222  includes a locking element  226  and an elongate pawl base  248  which are symmetrically constructed having a pair of pawl teeth  250 ,  252  and cantilever arms  254 ,  256  on each side thereof. First pawl tooth  250  includes first and second pawl tooth surfaces  250   a ,  250   b  facing first aperture  217  and block surface  221 , respectively. Similarly, second pawl tooth  252  includes first and second pawl tooth surfaces  252   a ,  252   b  facing second aperture  219  and block surface  221 , respectively. Cantilever arm  254  extends towards first aperture  217  and terminates at a first free end  254   a . Cantilever arm  256  extends towards second aperture  219  and terminates at a second free end  256   a.    
     Hinge  224  is positioned on and extends from a shoulder  225  of strap body  212 . Hinge  224  defines the closed ends of a first notch  260 , opening towards first aperture  217 , and a second notch  262 , opening towards second aperture  219 . Shoulder  225  forms a first rotation-stop surface  225   a  across first notch  260  from cantilever arm  254  and a second rotation-stop surface  225   b  across second notch  262  from second cantilever arm  256 . Stop surfaces  225   a  and  225   b  are formed having a pronounced taper so that stop surface  225   a  faces both first aperture  217  and block surface  221  while stop surface  225   b  faces both second aperture  219  and block surface  221 . Stop surfaces  225   a  and  225   b  limit the rotation of pawl  222  due to strap insertion and also provide a surface for facilitating the wedging of pawl  222  between shoulder  225  and strap body  212  so as to further compress strap body  212  against block surface  221 . Cantilever arms  254 ,  256  are designed so that upon rotation of locking element  226 , the free end  254   a ,  256   a  of the arm  254 ,  256  not engaging the strap body  212  extends over and against its opposite rotation stop surface  225   a ,  225   b  to thereby close its respective notch  260 ,  262 . Upon the attempted withdrawal of strap body  212 , pawl  222  is pulled along the stop surface of the closed notch towards the strap body and thus enhances the resistance to strap withdrawal. The resultant force F acting on pawl  222  is shown in FIG. 15 to be acting generally along the engaged stop surface. 
     Referring now to FIGS. 16-19, cable tie  210 ′, yet still another embodiment of the present invention, is shown. Similar numbering relates to similar components previously described. Cable tie  210 ′ is a bi-directional cable tie exhibiting enhanced resistance to withdrawal forces by providing an undercut to the locking teeth on the pawl for engaging the locking teeth of the strap body. The operation of pawl  222 ′ and its locking engagement with strap body  212 ′ is generally as previously described. Cable tie  210 ′ is generally integrally formed of a suitable molded plastic such as nylon. 
     Locking pawl  222 ′ of cable tie  210 ′ provides a chevron-shaped top surface  270 ′ in undeflected facing opposition to blocking surface  221 ′. The chevron-shape of top surface  270 ′ provides an undercut to the tooth engaging surfaces  250   b ′ and  252   b ′ of locking teeth  250 ′ and  252 ′, respectively, for increasing the locking effectiveness of locking pawl  222 ′. In this embodiment, tooth engaging surfaces  250   b ′ and  252   b ′ face both blocking surface  221 ′ and apertures  217 ′ and  219 ′, respectively. The chevron-shape of top surface  270 ′ is desirably formed by transversely-spacing locking teeth  250  and  252  across passageway  220 ′ as shown in FIGS. 16-19 so that the tooth engaging surfaces  250   b ′ and  252   b ′ have uninhibited exposure to apertures  217 ′ and  219 ′, respectively. Furthermore, the present invention contemplates providing a third locking tooth  258 ′ having a similar size, shape, and orientation as locking tooth  250 ′ for providing transversely-uniform resistance forces against strap body  212 ′. Desirably, the transverse dimension of locking teeth  250 ′ and  258 ′ are about the same as that of locking tooth  252 ′. 
     While the preferred embodiment of the present invention has been shown and described, it will be obvious in the art that changes and modifications may be made without departing from the teachings of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.