Abstract:
Locking fastener consisting of a threaded fastener having a head of noncircular contour, a lock plate having an opening in which the head of the fastener is received and constrained from rotating, and a retaining screw threadedly attached to the head of the fastener to retain the lock plate in position on the head. In the disclosed embodiments, the retaining screw is a tamper-proof security screw that requires a special tool or key for installation and removal. The fastener is particularly suitable for use in securing covers to utility boxes, and an adapter is included for use on existing boxes.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention pertains generally to locking fasteners and, more particularly, to a locking fastener which is tamper-proof. 
         [0003]    2. Related Art 
         [0004]    Locking fasteners are used in a variety of applications to prevent threaded fasteners from working loose due to vibration, and examples of such fasteners are found in U.S. Pat. Nos. 4,734,001, 4,906,150, 5,395,192, 5,674,034, and 7,708,509. Even in stationary structures such as underground utility boxes, vibrations in the earth can cause screws and the like to work loose. 
         [0005]    With underground electrical boxes, there is a further problem of thieves removing the covers from such boxes and pulling hundreds of feet of copper wire from conduits running from the boxes. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0006]    It is, in general, an object of the invention to provide a new and improved locking fastener. 
         [0007]    Another object of the invention is to provide a locking fastener of the above character which overcomes the limitations and disadvantages of locking fasteners heretofore provided. 
         [0008]    These and other objects are achieved in accordance with the invention by providing a locking fastener which comprises a threaded fastener having a head of noncircular contour, a lock plate having an opening in which the head of the fastener is received and constrained from rotating, and a retaining screw threadedly attached to the head of the fastener to retain the lock plate in position on the head. 
         [0009]    In the disclosed embodiments, the retaining screw is a tamper-proof security screw that requires a special tool or key for installation and removal. The fastener is particularly suitable for use in securing covers to utility boxes, and an adapter is included for use on existing boxes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an exploded isometric view of one embodiment of tamper-proof locking fastener incorporating the invention. 
           [0011]      FIG. 2  is an enlarged cross-sectional view taken along line  2 - 2  of  FIG. 1 , showing the fastener in an assembled state. 
           [0012]      FIG. 3  is an exploded isometric view of another embodiment of tamper-proof locking fastener incorporating the invention. 
           [0013]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3 , showing the fastener in an assembled state. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In  FIGS. 1 and 2 , the invention is illustrated in conjunction with an underground enclosure  11  of a type commonly utilized for housing electrical equipment. This enclosure has a generally rectangular, five-sided body or box  12  and a removable lid or cover  13 . The cover fits into a recessed area toward the top of the box, with the peripheral portion of the cover resting on a shoulder or ledge  14  that extends about the inner periphery of the box. The cover is secured to the box by cap screws or bolts which pass through counterbored openings  16  near diagonally opposite corners of the cover and are threadedly received in metal brackets  17  in corresponding corners of the box. Enclosures of this type are typically cast of a material such as polymer concrete, and in the embodiment illustrated, the end portions of the metal brackets are cast into the side wall of the box. 
         [0015]    The fastener comprises a cap screw or bolt  19 , a lock plate  21 , and a retaining screw  22 . The cap screw has a hexagonal head  23  and a threaded shank  24 , with an axially extending threaded bore  26  opening through the upper side of the head. 
         [0016]    The lock plate has a circular body  27 , with a 12-point central opening  28  and a positioning tab  29 . The opening is such that when the lock plate is placed on the head of the cap screw, the head is received in the opening in a non-rotational locking relationship. The tab extends radially or laterally from the circular body for abutting engagement with an object to prevent rotation of the lock plate. The plate also has a small threaded opening  31  at the base of the tab for receiving a tool (not shown) for use in placing the lock plate on the head of a screw in a recessed opening where fingers cannot reach. 
         [0017]    In the embodiment illustrated, an axially extending slot  32  having a contour corresponding to tab  29  opens through the side wall  33  of the counterbored section  34  of the opening  16  in cover  13 . 
         [0018]    Retaining screw  22  has a flanged head  36  of greater diameter than the opening in the lock plate and a threaded shank  37  that is received in the threaded bore in the head of the cap screw. The retaining screw is tamper-proof in that it has a socket  38  in the head that requires a special tool or key (not shown) for insertion and removal of the screw. Cleats  39  are provided on the under side of the head for binding engagement with a surface against which the screw is tightened. 
         [0019]    In use, cover  13  is positioned on enclosure box  12  with opening  16  aligned with a threaded opening  41  in bracket  17 . Cap screw  19  is inserted into opening  16  and threaded into opening  41 , then tightened to secure the cover to the box, with the head of the screw bearing against the bottom wall  42  of counterbore  34 . Lock plate  21  is then inserted into the counterbore, with the head of the screw being received in the opening  28  in the plate and tab  29  extending into slot  32  to prevent rotation of the lock plate and screw. Retaining screw  22  is then installed in the threaded bore  26  in the head of the cap screw and tightened to bring cleats  39  into binding engagement with the top surface of the cap screw and/or lock plate, depending upon the relative thicknesses of the two. 
         [0020]    Once installed, the locking fasteners prevent the screws that secure the cover to the box from working loose, and the tamper-proof retaining screws prevent the cover screws from being removed without a special tool or key that matches the drive sockets in the heads of the retaining screws. 
         [0021]    The embodiment illustrated in  FIGS. 3 and 4  is generally similar to the embodiment of  FIGS. 1 and 2 , and like reference numerals designate corresponding elements in the two embodiments. Here again, the fastener includes a cap screw or bolt  19 , a lock plate  21  that prevents the cap screw from working loose, and a tamper-proof retaining screw  22  that keeps the lock plate on the cap screw and the fastener secured in place. In this embodiment, however, the cap screw has a 12-point flanged head  44  rather than a 6-point hexagonal head. 
         [0022]    In addition to the cap screw, lock plate and retaining screw, the embodiment of  FIGS. 3 and 4  also includes an insert or adapter  46  for use in counterbores which do not have a slot for a lock tab. This allows the fastener to be used with existing enclosures that do not have a tab slot as well as enclosures which are manufactured with the slot or modified by milling a slot into them. 
         [0023]    The insert has a generally cylindrical body  47  with an annular side wall  48  and a bottom wall  49 . A clearance hole  51  for the shank of the cap screw is formed in the bottom wall, and an axially extending slot  52  opens inwardly through the side wall for receiving the tab on the lock plate. The insert is fabricated of a relatively rigid plastic material and has a diameter and length corresponding to the diameter and depth of the counterbore in which the fastener is to be installed. 
         [0024]    In use, the insert is press fit or hammered into the counterbore and thereby constrained against rotation. The cap screw is then passed through the openings in the bottom walls of the insert and counterbore, threaded into the enclosure box and tightened to secure the cover to the box, with the head of the screw bearing against the bottom wall of the insert and clamping it against the bottom wall of the counterbore. The lock plate and retaining screw are then installed in the manner described above to prevent loosening of the cap screw and unauthorized removal of the cover. 
         [0025]    The invention has a number of important features and advantages. The retaining screw provides a straightforward yet highly effective way of keeping the lock plate on the cap screw to prevent the cap screw from loosening, and being a tamper-proof security screw, the retaining screw also prevents unauthorized removal of the fastener. 
         [0026]    While the invention has been described with specific to counterbore screws and bolts, it will be understood that the retainer can be employed with other types of locking fasteners including teardrop-shaped lock plates and lock plates that bridge between two or more fasteners. 
         [0027]    It is apparent from the foregoing that a new and improved tamper-proof locking fastener has been provided. While only certain presently preferred embodiments have been described in detail, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims.