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BACKGROUND 
     1. Field of the Invention 
     This invention relates to destructible locking devices of the type employed to releasably interconnect mating components of security devices. Such security devices are widely employed by public utilities to secure meters, supply valves, etc. against unauthorized access. 
     2. Description of the Prior Art 
     The operating mechanism of a conventional utility meter is typically enclosed within a transparent dome which in turn is removably attached to the cover of a box-shaped housing. The cover and dome have circular rims that are held in an axially aligned abutting relationship by a channel-shaped split retaining ring. The ends of the retaining ring are configured as mating components which are releasably interconnected in a confronting relationship by locks of varying design. 
     One such lock of the destructible type is disclosed in U.S. Pat. No. 5,161,838 (Ely et al.), where the mating end components of the split retaining ring are captured between an enlarged head at one end of a stud, and a cap-shaped housing secured to the opposite end of the stud. The stud is further provided with a frangible section adjacent its head which is designed to shear under a compressive load. The load is axially applied by a tool engaging both the cap shaped housing and the head of the stud. 
     One drawback with this type of lock is that it may be destructively disassembled by any tool capable of exerting the required compressive force. Thus, where multiple utility systems employ locks of this type, one systems&#39; tools can be used to compromise the security of the other systems&#39; meters. 
     A lock of this type also requires a relatively high level of compressive force to shear the frangible stud section. This in turn requires utility personnel to carry tools that are heavy, cumbersome, and have unduly long operating cycles, typically involving the use of wrenches or the like to operate screw actuated force exerting mechanisms. 
     A general objective of the present invention is the provision of an improved destructible locking device which either obviates or at least significantly minimizes the above described drawbacks of the prior art. 
     A specific objective of the present invention is the provision of a locking device which is uniquely configured to be destructively disassembled only by a tool having a mating uniquely configured design. 
     A companion objective of the present invention is the provision of a locking device which may be destructively disassembled by the application of only a relatively modest torque. 
     SUMMARY OF THE INVENTION 
     The locking device of the present invention is useful, for example, in releasably interlocking two confronting components having aligned openings, typically the ends of a split ring used to secure the transparent dome of a utility meter to the cover of a meter box. In one embodiment to be described hereinafter in greater detail, the locking device includes a hollow cap and a pin having an enlarged head at one end and a nose at its opposite end. The pin is configured and dimensioned to extend through the aligned openings of the confronting components, with its nose received in permanent interlocked engagement in the cap, thereby securely capturing the confronting components between the cap and the enlarged head of the pin. The nose has a frangible portion which may be severed by twisting the nose relative to the pin head. The locking device may be destructibly disassembled by subjecting the pin to a torque sufficient to shear the frangible nose portion. A specially configured tool is engageable with mating specially configured pin segments to effect the required torque application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of a locking device and tool in accordance with the present invention will now be described in detail with reference to the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a typical utility meter having a transparent dome removably attached to the meter box cover by a split retaining ring, with the ends of the retaining ring being secured by a locking device in accordance with the present invention; 
     FIG. 2 is a sectional view on an enlarged scale taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged longitudinal sectional view through the locking device of the present invention, showing the locking device in its locked condition; 
     FIG. 4 is a longitudinal sectional view of the locking device prior to its assembly into the locked condition shown in FIG. 3; 
     FIGS. 5 and 6 are cross sectional views taken respectively along lines  5 — 5  and  6 — 6  of FIG. 4; 
     FIG. 7 is a plan view of a tool used to destructively disassemble the locking device; 
     FIG. 8 is a sectional view on an enlarged scale taken along line  8 — 8  of FIG. 7; 
     FIGS. 9 and 10 are cross sectional views taken along line  9 — 9  and  10 — 10  of FIG. 8; 
     FIG. 11 is a view similar to FIG. 3 showing the tool operatively positioned to destructively disassemble the locking device; 
     FIG. 12 is an exploded view showing the locking device in its destructively disassembled state; 
     FIG. 13 is a longitudinal sectional view of an alternative embodiment of a locking device in accordance with the present invention; 
     FIG. 14 is a view similar to FIG. 13 showing the locking device after it has been destructively disassembled; 
     FIG. 15 is a cross sectional view showing a seal closing the end of the passageway in the locking pin; 
     FIG. 16 is a perspective view of the seal shown in FIG. 15; 
     FIG. 17 is an illustration of a alternative seal useful with the locking device of the present invention; 
     FIG. 18 is an end view of the seal shown in FIG. 17; 
     FIG. 19 is a view showing the locking device of the present invention enclosed within a protective plastic cap; 
     FIG. 20 is a side view of the assembly shown in FIG. 19; 
     FIG. 21 a  is an exploded view of an alternative embodiment of a locking device in accordance with the present invention; 
     FIG. 21 b  shows the components of FIG. 21 a  in their assembled state; 
     FIG. 22 a  is an exploded view still another embodiment of a locking device in accordance with the present invention; and 
     FIG. 22 b  is a view of the components shown in FIG. 22 a  in their assembled state. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference initially to FIGS. 1 and 2, a conventional utility meter is shown at  10  comprising a meter box  12  closed by a cover  14  which supports a transparent dome  16  enclosing the meter mechanism (not shown). The cover  14  and dome  16  have circular flanges  14   a ,  16   a  which are secured in a confronting abutting relationship by a channel shaped split retaining ring  18  The ends of the ring are bent outwardly to provide first and second mating components  20 ,  22 . 
     As can best be seen by further reference to FIG. 3, the mating components  20 ,  22  are provided respectively with first and second openings  20   a ,  22   a  extending between inner and outer surfaces  20   b ,  20   c  and  22   b ,  22   c.    
     One embodiment of a locking device in accordance with the present invention comprises a receiving element in the form of a hollow cap  24  and a pin  26 . With additional reference to FIGS. 4-6, it will be seen that the cap  24  has an interior chamber  28  accessible via an open mouth  30 . An interior groove  32  contains a resilient snap ring  34 . A cylindrical sleeve  36  communicates with the mouth  30  and protrudes axially from an external shoulder  38 . The sleeve  36  is externally provided with a groove  40  which coacts with an optional resilient O-ring  42  to detachably retain the cap in its assembled position on the mating ring component  20  as shown in FIG. 4, with the sleeve  36  protruding through the opening  20   a , and with the shoulder  38  bearing against the outer surface  20   c.    
     The pin  26  has an enlarged head  44  at one end and a nose  46  at its opposite end. A passageway  48  extends axially through the pin. The pin is externally configured to provide a shoulder  50  axially outboard of a V-shaped groove  52 , and a circular groove  54  inboard of a shoulder  56 . The groove  52  provides a demarcation line between the nose  46  and the remainder of the pin, and has a depth sufficient to define a frangible portion of the pin. The groove  54  coacts with an optional second resilient O-ring  58  to detachably retain the pin  26  in its assembled position extending through the opening  22   a  in ring component  22 , with the shoulder  56  abutting against the outer surface  22   c.    
     The pin is internally configured to provide axially separated torque receiving sections  60 ,  62  located respectively in the nose  46  and head  44 . As shown in FIG. 5, the torque receiving section  60  has specially configured flutes indicated typically at  64 . As shown in FIG. 6, the torque receiving section  62  has differently configured flutes indicated typically at  68 . 
     In its initial unlocked state, as shown in FIG. 4, the cap  24  and pin  26  of the locking device are axially separated and detachably retained, respectively on the ring components  20 ,  22  by the optional O-rings  42 ,  58 . The lock is assembled by simply pressing the pin and cap together, thereby causing the nose  46  to enter the cavity  28  via the sleeve  36  and mouth  30 , where the shoulder  50  is engaged by the snap ring  34  in a snap connection, thereby permanently securing the cap  24  to the nose  46 , as shown in FIG.  3 . 
     Referring now to FIGS. 7-10, a tool  70  is provided for destructively disassembling the locking device. The tool includes first and second relatively rotatable dies  72 ,  74 . As shown in FIG. 9, the first die  72  is externally configured with ridges  76  specially configured to coact in mating interengagement with the internal flutes  64  in the nose  46  of the lock pin  26 . Similarly, as shown in FIG. 10, the second die  74  is externally configured with ridges  78  specially configured to coact in mating interengagement with the internal flutes  68  in the head  44  of the lock pin  26 . 
     The second die  74  is pinned or otherwise fixed to an outer handle  80 , and the first die  72  is similarly secured to a bushing  82  fixed with respect to an inner handle  84 . 
     The handles  80 ,  84  are separated by a washer  86  and are resiliently retained in the open position shown in FIG. 7 by a spring  88 . An external washer  90  and lock nut  92  completes the assembly. 
     In order to destructively disassemble the locking device, the tool  70  is operatively positioned as shown in FIG. 11, with the ridges  76  of the first die  72  mechanically interengaged with the flutes  64  of the torque receiving section  60  in the nose  46 , and with the ridges  78  of the second die  74  mechanically interengaged with the flutes  68  of the torque receiving section  62  in the head  44 . The handles  80 ,  84  are then closed in the direction of the arrows in FIG. 7, thereby contrarotating the first and second dies  72 ,  74 . A corresponding rotation is thus imparted to the nose  46  and head  44 , causing the pin to torsionally shear at the groove  52 . 
     As shown in FIG. 12, this results in the pin being broken apart into two segments  26   a ,  26   b . Segment  26   a  remains captured within the cap  24 , the latter being disengageable from ring component  20  by simply overcoming the yieldable retaining force exerted by O-ring  42 . Pin section  26   b  is similarly disengageable from ring component  22 . 
     With references to FIGS. 13 and 14, it will be seen that a modified cap  24 ′ may be provided with a second opening  94  which preferably is in alignment with the mouth  30  through which the nose  46  is received in the chamber  28 . When the locking device is destructively disassembled as previously described, the nose  46  can be ejected from the cap chamber  28  via opening  94  as shown in FIG.  14 . Thus, the cap  24 ′ can be preserved for reuse with another locking pin after the fractured pin segment has been disengaged from the ring component  22  and replaced by a fresh pin. 
     In order to further enhance security, a tamper evident seal may be applied to the locking device. For example, as shown in FIGS. 15 and 16, the seal may comprise a plastic disk  96  applied to the head  44  of the pin  26  at a position closing off the open end of passageway  48 . The disk may be held in place by integral resilient legs  98  configured and arranged to mechanically engage interior surfaces of the head  44 . In order to gain access to the passageway  48 , the disk must be broken and removed, thus providing visual evidence that an attempt has been made to compromise the integrity of the locking device. 
     In the embodiment shown in FIGS. 17 and 18, an alternative embodiment of a seal  100  includes a wire  102  threaded through holes in the pin head  44  to extend across the entry end of the passageway  48 . The ends of the wire are permanently captured in a transparent plastic housing  104  of generally known design. Here again, in order to gain access to the passageway, the wire  102  must be cut or the plastic housing must be destroyed in order to remove the seal  100  from the locking device, thereby providing visual evidence of attempted tampering. 
     As shown in FIGS. 19 and 20, under certain circumstances it may be desirable to completely enclose the locking device. To this end, a suitably configured plastic cap  106  may be inserted over the locking device and mating ring components. 
     The locking device of the present invention is useful with security devices other than split retaining rings used to detachably couple meter domes to the covers of meter boxes. For example, FIGS. 21A and 21B illustrate a security device  106  of the type employed to retain the cover  108  of a meter box in a closed position with respect to the box sidewall  110 . The security device includes a housing  112  secured to the exterior of the box wall  110  by means of an internally accessible bolt  114  which extends through a reinforcing element  116  and through a hole in the box wall. The bolt is threaded into the base of the housing as at  118 . 
     A receiving element  120  in the form of a deadbolt is shiftable in a transverse passageway  122  in the housing  112  between an operative position overlapping the box cover  108 , as shown in FIG. 21B, and a retracted position as shown in FIG. 21A, and as indicated by the broken lines in FIG.  21 B. The deadbolt has a vertical passageway  124  which communicates with a vertical passageway  126  in the housing  112 . The deadbolt passageway  124  defines a chamber which is internally grooved to accept a resilient snap ring  128 . When the deadbolt is in its operative position with the passageways  124 ,  126  in mutual alignment, a lock pin of the type described previously may be inserted as shown, with the nose  46  of the lock pin captured in the deadbolt passageway  124  by the snap ring  128 . The deadbolt may then be retracted only by first destructively separating the nose  46  from the remainder of the pin, as described previously. 
     In FIGS. 22A,  22 B, a receiving element in the form of a gas plug  130  is shown threaded into the end of a supply pipe  132 . The plug has the usual multi faced neck  134  which is configured to be engaged and rotated by a wrench (not shown). The plug includes a blind bore  136  forming a chamber which is internally grooved to accept the snap ring  138 . A protective cap  140  is seated over the neck  134  and is rotatable with respect to the neck to thereby foil an attempt to rotate the plug by means of a wrench or other like tool. The cap is held in place by a lock pin as described previously, the nose  46  of which is again captured in the passageway  124  by the snap ring  138 . In order to remove the cap  140 , one must destructively separate the nose  46  from the remainder of the pin  26 , again as previously described. 
     In light of the foregoing, it will now be appreciated by those skilled in the art that the present invention offers significant advantages not available with prior art locking devices. Most importantly, by providing the pin  26  with torque receiving sections  60 ,  62  which are specially configured to coact with mating specially configured dies  72 ,  74  on the tool  70 , security is markedly enhanced by virtue of the fact that the locking device can only be destructively disassembled by a tool specially designed for that purpose. By varying the shapes and or orientations of the flutes of one or both of the torque receiving sections  60 ,  62 , a myriad of combinations can be developed, each being accessible only by tools specifically designed to do so. Other tools designed to work with other locks cannot be used. 
     Preferably, at least one and most preferably both of the torque receiving sections  60 ,  62  are located internally within the pin  26 , making it extremely difficult if not impossible to develop the torque required to shear the pin by externally applied means. 
     The lock is also resistant to tampering and destructive disassembly by axially directed forces. More particularly, with reference to FIG. 3, externally applied axial forces at “A” and “B” will cause the pin  26  and cap  24  to “bottom out” externally at the common annular interface denoted at “X”, thereby safeguarding the pin from axially induced shearing at groove  52 . A similar safeguard is provided in the event that a tool is inserted into the pin to axially exert a force at “C” together with an externally applied force “A”. In this case, the pin and cap will bottom out internally at the common conical interface “Y”, again safeguarding the pin from axially induced shearing at groove  52 . 
     Also, by appropriately configuring the shape and depth of the groove  52  in the shank of the pin, only a modest torque is required to effect shearing of the pin. Thus, the weight of the tool  70  can be reduced. Tool cycle time is also reduced to that required to simply close and reopen the handles  80 ,  84 . 
     Various changes may be made to the embodiments herein disclosed without departing from the spirit and scope of the claimed invention. By way of example only, and without limitation, the location and configuration of the torque receiving sections and the tool dies may be varied, as can the location and orientation of the notch or other equivalent feature defining the frangible pin section. Other arrangements for permanently coupling the cap to the nose of the pin are possible, including for example mechanically interengageable surfaces integrally formed on the pin and cap.

Summary:
A locking device is disclosed for interlocking two members having aligned openings extending therethrough. The device includes a hollow cap and a pin with an enlarged head at one end and a nose at the opposite end. The pin is insertable through the aligned openings of the members, with its nose received in interlocked engagement within the cap, and with the two members captured between the cap and the enlarged head of the pin. A frangible portion of the pin is severable in response to relative rotation between its nose and enlarged head to thereby destructively disassemble the locking device.