Abstract:
Captive fasteners are provided that may be used with guards that cover particular areas of a machine. The fasteners are attached to the guards so that they remain with the guard when the guard is removed from the machine. In order to make it easier to reinstall the guard onto a machine when the guard is misaligned, the fasteners can move along a slotted opening in the guard.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to fasteners and more particularly to captured hardware. 
         [0002]    Fasteners are used in numerous applications to attach various components together. Typically, a fastener has at least a threaded portion and a plurality of bearing surfaces attached thereto. The bearing surfaces are designed to receive torque from a tool, such as a socket or wrench, which is used to tighten or loosen the fastener. In a conventional fastener, such as a nut, the fastener may have internal threads and six bearing surfaces oriented in a hexagonal shape around the internal threads. Other fasteners may have external threads, such as a screw. Fasteners may also have numerous types of bearing surfaces, including external heads with four, eight or any other number of side bearing surfaces and internal bearing surfaces, such as screw driver straight blades or Phillips drive surfaces. 
         [0003]    One application that fasteners are used for his attaching operator guards on various types of machines and other apparatus to prevent an operator from accessing particular areas of the machine during operation or to protect such areas of the machine from coming into contact with foreign objects during use. Typically, machines are designed with certain areas that require frequent access for maintenance or other reasons. However, when the machine is in operation, it may be desirable to prevent access to these areas because of safety concerns or other reasons. To address these needs, manufacturers of machinery often provide removable guards, or other apparatus, to cover particular areas of the machine. Normally, these guards are attached to the machine with various types of fasteners with conventional bearing surfaces. Thus, when an operator needs to gain access to a particular area covered by the removable guard, the operator can use a conventional torque tool to loosen the fasteners and remove the guard from the covered area. After the operator has finished whatever work is needed within the guarded area, the operator reinstalls the guard in the original location on the machine and tightens the fasteners to reattach the guard. 
         [0004]    Although guards may be attached to a machine in numerous ways, one common attachment design includes a pattern of nuts that have been welded to the frame of the machine. The guards may have a pattern of holes through the guard that matches the pattern of welded nuts. The guard may then be positioned against the machine frame so that the holes in the guard lineup with the welded nuts. Conventional screws can then be inserted through the holes in the guard and tightened into the welded nuts to secure the guard to the machine. Alternatively, the machine may be provided with permanently attached threaded studs that extend out toward the guard. The guard may then be placed over the studs so that the studs extend through the holes in the guard. In this arrangement, conventional nuts may be tightened onto the studs to secure the guard onto the machine. 
         [0005]    In some cases, it may be desirable to provide slotted openings in the guard instead of round holes. The primary reason for using slotted openings is to make it easier for an operator to remove and reinstall the guard onto the machine frame. Round holes through the guard can make it difficult and time-consuming to remove and reinstall a guard onto a machine when the pattern of holes through the guard do not closely match the pattern of nuts or studs attached to the machine. This situation can occur for a number of reasons, such as dimensional variations that occur during manufacturing and bending or deformation that can occur during use of the machine to the machine frame, the permanently attached nuts or studs or to the guard. Lining up the holes in the guard to the nuts or studs attached to the machine also becomes increasingly more challenging when the number of fasteners is increased. For example, a guard that uses eight fasteners and eight corresponding guard holes and welded nuts will typically be significantly more difficult to line up and attach than a guard that only uses two fasteners and two corresponding guard holes and welded nuts. Slotted openings through the guard greatly reduce the difficulty and time required to remove and reinstall a guard by providing a greater range of positions that the guard can be lined up to the machine frame and still permit the fasteners to engage the permanently attached to nuts or studs through the guard openings. 
         [0006]    The fasteners that are used to attach a guard to a machine oftentimes are conventional fasteners that are separate from the guard and the machine. This is a common choice when designing a guard and attachment arrangement because it is simple to manufacture and easy to use. However, there are several problems with the use of loose fasteners that are not attached in any way to the guard. One common problem with this design is that the fasteners can be lost by the operator when the guard is removed for maintenance within the guarded area. When this occurs, the operator may be forced to stop using the machine until replacement fasteners are acquired. This can be expensive because operational time with the machine is lost while the operator searches for the lost fasteners or new fasteners are procured. If the fasteners are special fasteners that must be purchased from the manufacturer or other specialty supplier, the replacement fasteners may also be costly to purchase. In addition, there is a risk that the lost fasteners may fall into mechanisms of the machine. Potentially, this can cause even more damage to the machine if the lost fasteners become entangled with moving parts of the machine. Alternatively, an operator may choose to continue using the machine without the guard in place to avoid the time and expense involved in replacing the lost fasteners. However, this can be dangerous if the guard is designed to protect the operator from moving or hot parts within the guarded area. On the other hand, if the guard is designed to protect an area of the machine from coming into contact with foreign objects during use, the operator risks damaging the machine or causing other damage by operating machine without the guard in place. 
         [0007]    Accordingly, the inventor believes it would be desirable to provide a fastener that can be attached to a guard or other apparatus and is movable along a slot in the guard or apparatus. 
       SUMMARY 
       [0008]    Captured fasteners are described that may be attached to an apparatus, such as a guard. The fasteners may be provided with internal threads, such as a nut, or with external threads, such as a screw. The fasteners are provided with a sleeve that has a slot that corresponds to a slot in the guard. Therefore, the nut or screw can move along the length of the slot to make it easier to attach the guard to a machine. Additional details and advantages are described below in the detailed description. 
         [0009]    The invention may include any of the following aspects in various combinations and may also include any other aspect described below in the written description or in the attached drawings. 
         [0010]    A fastener, comprising: 
         [0000]    a plurality of wrench bearing surfaces;
 
a threaded portion coaxial with and rotationally fixed to the wrench bearing surfaces;
 
a first torque bearing surface rotationally fixed to the wrench bearing surfaces;
 
a sleeve comprising an attachment surface adapted to fixedly attach the sleeve to an apparatus, a second torque bearing surface oppositely disposed from the attachment surface, a slotted opening extending through the second torque bearing surface, and an undercut space larger in size than the slotted opening disposed under the slotted opening between the second torque bearing surface and the attachment surface, the second torque bearing surface being larger in size than the slotted opening and being adapted to engage the first torque bearing surface;
 
an insert portion extending through the slotted opening, the insert portion being coaxial with the wrench bearing surfaces, the insert portion being approximately equal in size to a width of the slotted opening to minimize lateral movement of the insert portion within the slotted opening, and the insert portion being smaller in size to a length of the slotted opening to allow movement of the insert portion along the length of the slotted opening;
 
a retaining member longitudinally restrained to the wrench bearing surfaces when the wrench bearing surfaces are moved longitudinally and not rotated, the retaining member disposed within the undercut space and being larger in size than a width of the slotted opening;
 
wherein the wrench bearing surfaces, the threaded portion, the first torque bearing surface, and the insert portion are prevented from being separated from the sleeve by the retaining member when the wrench bearing surfaces are not rotated, and longitudinal force is transmitted to the apparatus through the first torque bearing surface, the second torque bearing surface, the sleeve and the attachment surface when the wrench bearing surfaces are tightened.
 
         [0011]    The fastener wherein the wrench bearing surfaces, the threaded portion, the first torque bearing surface, the insert portion and the retaining member comprise an integral nut, the threaded portion comprising internal threads. 
         [0012]    The fastener further comprising a washer disposed within the undercut space between the retaining member and the slotted opening and being larger in size than the width of the slotted opening. 
         [0013]    The fastener wherein the retaining member is a flange on an inner sleeve, the inner sleeve being longitudinally restrained to the wrench bearing surfaces when the wrench bearing surfaces are moved longitudinally and not rotated. 
         [0014]    The fastener wherein the inner sleeve comprises inner threads, the threaded portion of the screw being threadable through the inner threads of the inner sleeve. 
         [0015]    The fastener wherein the wrench bearing surfaces, the threaded portion and the first torque bearing surface comprise an integral screw, the threaded portion comprising external threads, the screw further comprising a shaft portion disposed between the first torque bearing surface and the threaded portion, the shaft portion being smaller in diameter than the inner threads of the inner sleeve, the shaft portion thereby being slidable through the inner threads. 
         [0016]    The fastener wherein the inner sleeve comprises a contact surface at a first end of the inner sleeve disposed away from the first torque bearing surface, the contact surface being adapted to contact a surface of the apparatus when the sleeve is fixedly attached to the apparatus, the contact surface being larger in size than a width of an apparatus slotted opening extending through the apparatus which the fastener is adapted for, the inner sleeve thereby being prevented from extending through the apparatus slotted opening when the sleeve is fixedly attached to the apparatus. 
         [0017]    The fastener wherein a width of the contact surface is approximately equal in size to a width of the undercut space to minimize lateral movement of the inner sleeve within the sleeve. 
         [0018]    The fastener wherein a length between the contact surface and a second end of the inner sleeve disposed toward the first torque bearing surface is at least as long as a distance between the attachment surface and the slotted opening, an end portion of the inner sleeve adjacent the second end thereby protruding through at least a portion of the slotted opening when the contact surface contacts the surface of the apparatus, the end portion forming the insert portion. 
         [0019]    The fastener wherein the end portion comprises opposing flat sides engaged with the width of the slotted opening, the inner sleeve thereby being rotationally fixed to the sleeve. 
         [0020]    The fastener wherein the end portion extends along a length of the inner sleeve greater than a depth of the slotted opening, the end portion thereby being slidable through the slotted opening and the second end of the inner sleeve being extendable past the second torque bearing surface, the opposing flat sides extending an entire length that the end portion is slidable through the slotted opening. 
         [0021]    The fastener wherein the flange is disposed at the first end of the inner sleeve thereby forming the contact surface and the end portion extends from the second end to the flange. 
         [0022]    The fastener wherein the inner threads of the inner sleeve are disposed adjacent the second end, the inner sleeve further comprising an internal portion disposed from the inner threads to the first end and being larger in size than the threaded portion, the threaded portion thereby being slidable through the internal portion. 
         [0023]    The fastener wherein a combined length of the shaft portion and the end portion is within a 25% range of a length of the threaded portion. 
         [0024]    The fastener wherein the threaded portion comprises external threads and the retaining member is a flange on an inner sleeve, the inner sleeve being longitudinally restrained to the wrench bearing surfaces when the wrench bearing surfaces are moved longitudinally and not rotated, the inner sleeve comprising a contact surface at a first end of the inner sleeve disposed away from the first torque bearing surface, the contact surface being adapted to contact a surface of the apparatus when the sleeve is fixedly attached to the apparatus, a length between the contact surface and a second end of the inner sleeve disposed toward the first torque bearing surface being at least as long as a distance between the attachment surface and the slotted opening, and an end portion of the inner sleeve adjacent the second end thereby protruding through at least a portion of the slotted opening when the contact surface contacts the surface of the apparatus, the end portion forming the insert portion, the end portion comprising opposing flat sides engaged with the width of the slotted opening, the inner sleeve thereby being rotationally fixed to the outer sleeve, the end portion extending along a length of the inner sleeve greater than a depth of the slotted opening, the end portion thereby being slidable through the slotted opening and the second end of the inner sleeve being extendable past the second torque bearing surface, and the opposing flat sides extending an entire length that the end portion is slidable through the slotted opening. 
         [0025]    The fastener wherein the wrench bearing surfaces, the threaded portion and the first torque bearing surface comprise an integral screw, the inner sleeve comprising inner threads, the threaded portion of the screw being threadable through the inner threads of the inner sleeve. 
         [0026]    The fastener wherein the screw further comprises a shaft portion disposed between the first torque bearing surface and the threaded portion, the shaft portion being smaller in diameter than the inner threads of the inner sleeve, the shaft portion thereby being slidable through the inner threads, the inner threads of the inner sleeve being disposed adjacent the second end, the inner sleeve further comprising an internal portion disposed from the inner threads to the first end and being larger in size than the threaded portion, the threaded portion thereby being slidable through the internal portion. 
         [0027]    The fastener wherein a combined length of the shaft portion and the end portion is within a 25% range of a length of the threaded portion. 
         [0028]    The fastener wherein the threaded portion comprises external threads and the retaining member is a flange on an inner sleeve, the inner sleeve being longitudinally restrained to the wrench bearing surfaces when the wrench bearing surfaces are moved longitudinally and not rotated, the inner sleeve comprising a contact surface at a first end of the inner sleeve disposed away from the first torque bearing surface, the contact surface being adapted to contact a surface of the apparatus when the sleeve is fixedly attached to the apparatus, the contact surface being larger in size than a width of an apparatus slotted opening extending through the apparatus which the fastener is adapted for, the inner sleeve thereby being prevented from extending through the apparatus slotted opening when the sleeve is fixedly attached to the apparatus, a width of the contact surface being approximately equal in size to a width of the undercut space to minimize lateral movement of the inner sleeve within the sleeve. 
         [0029]    The fastener wherein a length between the contact surface and a second end of the inner sleeve disposed toward the first torque bearing surface is at least as long as a distance between the attachment surface and the slotted opening, an end portion of the inner sleeve adjacent the second end thereby protruding through at least a portion of the slotted opening when the contact surface contacts the surface of the apparatus, the end portion forming the insert portion and comprising opposing flat sides engaged with the width of the slotted opening, the inner sleeve thereby being rotationally fixed to the sleeve, the end portion extending along a length of the inner sleeve greater than a depth of the slotted opening, the end portion thereby being slidable through the slotted opening and the second end of the inner sleeve being extendable past the second torque bearing surface, the opposing flat sides extending an entire length that the end portion is slidable through the slotted opening, the inner sleeve further comprising inner threads, the threaded portion of the screw being threadable through the inner threads of the inner sleeve, and further comprising a shaft portion disposed between the first torque bearing surface and the threaded portion, the shaft portion being smaller in diameter than the inner threads of the inner sleeve, the shaft portion thereby being slidable through the inner sleeve, the inner threads of the inner sleeve being disposed adjacent the second end, the inner sleeve further comprising an internal portion disposed from the inner threads to the first end and being larger in size than the threaded portion, the threaded portion thereby being slidable through the internal portion. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0030]    The invention may be more fully understood by reading the following description in conjunction with the drawings, in which: 
           [0031]      FIG. 1  is a top perspective view of a nut intended to be fixedly attached to an apparatus; 
           [0032]      FIG. 2  is a bottom perspective view of the nut; 
           [0033]      FIG. 3  is a cross-sectional view of the nut, showing the width of the slot in the sleeve; 
           [0034]      FIG. 4  is a cross-sectional view of the nut, showing the length of the slot in the sleeve; 
           [0035]      FIG. 5  is a cross-sectional view of a screw intended to be fixedly attached to an apparatus, showing the width of the slot in the sleeve; 
           [0036]      FIG. 6A  is a top plan view of a sleeve and inner sleeve; 
           [0037]      FIG. 6B  is a perspective view of the sleeve and the inner sleeve, showing the inner sleeve fully collapsed within the sleeve; 
           [0038]      FIG. 6C  is a perspective view of the sleeve and the inner sleeve, showing the inner sleeve fully telescoped through the slotted opening in the sleeve; 
           [0039]      FIG. 7  is a cross-sectional view of the screw, showing the length of the slot in the sleeve; 
           [0040]      FIG. 8  is a bottom perspective view of the screw; 
           [0041]      FIG. 9  is a cross-sectional perspective view of the screw, showing the screw and inner sleeve telescoped out of the sleeve; 
           [0042]      FIG. 10  is a cross-sectional perspective view of the screw, showing the screw telescoped out of the sleeve and the inner sleeve completely within the sleeve; 
           [0043]      FIG. 11  is a cross-sectional perspective view of the screw, showing the screw with a reduced body diameter bolt and an outer sleeve and the guard attached to a machine; and 
           [0044]      FIG. 12  is a top perspective view of the screw, showing the screw with a captive inner sleeve (not visible) attached to a guard. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]    Referring now to the figures, and particularly to  FIGS. 1-4 , a nut fastener  20  is shown. The nut fastener  20  is designed to provide a captured nut  40  that may be attached to an apparatus  10 , such as a guard  10 . As shown in  FIGS. 3-4 , the nut fastener  20  may include a sleeve  22  that is permanently attached to a guard  10  by welding the attachment surface  24  of the sleeve  22  to the guard  10 . The sleeve  22  may be welded to the guard  10  either by welding around the outer circumference of the sleeve  22  or providing weld nubs  65  on the attachment surface  24  of the sleeve  22  (as shown in  FIG. 8 ). When weld nubs  65  are provided, the sleeve  22  may be attached to the guard  10  by simultaneously pressing the sleeve  22  against the guard  10  and applying electrical current to the sleeve  22 . This causes the weld nubs  65  to melt into the surface of the guard  10  and welds the sleeve  22  and guard  10  together. The guard  10  may be provided with a slotted opening  12  which a threaded stud may be inserted through. Typically, the threaded stud will be permanently attached to a machine, and the apparatus  10  that the nut fastener  20  is attached to will be a guard  10  designed to cover a particular area of the machine. The slotted opening  12  in the guard  10  typically has a width  14  that is approximately the same size of the threaded stud attached to the machine to minimize lateral movement between the guard  10  and the threaded machines stud. However, the length  16  of the slotted opening  12  in the guard  10  is longer than the size of the threaded machine stud so that the guard  10  and the stud can move relative to each other. 
         [0046]    The sleeve  22  also includes a slotted opening  26  that generally corresponds to the shape of the slotted opening  12  in the guard  10  so that the nut  40  can move along the length  16  of the slotted opening  26  as further described below. The size of the slotted opening  26  is the sleeve  22  may be larger than the slotted opening  12  in the guard  10  if desired to allow for the particular size of the insert portion  42  that is used. Accordingly, the slotted opening  26  in the sleeve  22  preferably has a width  28  that is approximately the same size as the insert portion  42  of the nut  40  to minimize lateral movement between the nut  40  and the sleeve  22 . The length  30  of the slotted opening  26  in the sleeve  22  may be longer than the size of the insert portion  42  of the nut  40  to allow movement of the nut  40  along the length  30  of the slotted opening  26 . The sleeve  22  also includes an undercut space  32  below the slotted opening  26  that is larger in size than the slotted opening  26 . Preferably, the undercut space  32  extends the entire length from the slotted opening  26  in the sleeve  22  to the attachment surface  24 . The undercut space  32  receives a retaining member  44  of the nut  40  which is larger than the insert portion  42  of the nut  40 . The retaining member  44  is also larger than the width  28  of the slotted opening  26  in the sleeve  22 . Thus, the retaining member  44  prevents the nut  40  from being separated from the sleeve  22 . Although the retaining member  44  may be formed and shaped in various ways, one desirable way to make the retaining member  44  is to initially form the retaining member  44  as a straight extension of the insert portion  42 . During assembly, the insert portion  42  and extended portion may be inserted through the slotted opening  26  in the sleeve  22  and the extended portion can be flared out by swaging. Preferably, the width  34  and the length  36  of the undercut space  32  are both larger than the slotted opening  26  by the same amount to accommodate the larger size of the retaining member  44  both along the width  34  and the length  36  of the undercut space  32 . 
         [0047]    The sleeve  22  further includes a second torque bearing surface  38  that is designed to engage with the first torque bearing surface  46  of the nut  40 . Thus, when the nut  40  is tightened onto a threaded stud attached to a machine or other apparatus, compressive force is transmitted between the first and second torque bearing surfaces  46 ,  38  and through the sleeve body  22  to the attachment surface  24 . The nut  40  may be provided with numerous torque bearing surfaces  48 , but conventional hexagonal-shaped bearing surfaces  48  as shown in  FIG. 1  may be used. The nut  40  also includes conventional internal threads  50  for engaging the external threads of a stud. A washer  52  may also be provided in the undercut space  32  between the retaining member  44  and the top  33  of the undercut space  32  to provide improved retention of the nut  40  within the sleeve  22  if desired. However, the washer  52  may be eliminated and the nut  40  may be directly swaged or staked within the undercut space  32  if a less expensive assembly is desired. 
         [0048]    It is now apparent that the nut fastener  20  provides a nut assembly  20  that can be permanently attached to a guard  10  and provides a range of movement for the nut  40  that can correspond to a slotted opening  12  in the guard  10 . As described, the sleeve  22  may be welded to the guard  10  so that the position of the slotted opening  26  in the sleeve  22  mates with the slotted opening  12  in the guard  10 . This allows the nut  40  to move along the length  16  of the slotted opening  12  in the guard  10 . Thus, the nut  40  can be threaded onto a threaded machine stud extending through the slotted opening  12  in the guard  10  regardless of where the threaded machine stud is located along the length  16  of the slotted opening  12 . As a result, the guard  10  may be easily attached to the machine even if the guard  10  is not perfectly aligned with the machine. The nut  40  is also captured and retained onto the guard  10  to prevent the nut  40  from being dropped and/or lost when the guard  10  is removed from the machine. This makes it easier to reinstall the guard  10  and more likely that an operator will it reinstall the guard  10  before using the machine. 
         [0049]    Turning to  FIGS. 5-12 , a screw fastener  60  is shown. The screw fastener  60  is designed to provide a captured screw  80  that may be attached to an apparatus  10 , such as the guard  10  described above. Thus, in contrast to the nut fastener  20  described above, the screw fastener  60  may be used to attach a guard  10  to a machine that is provided with threaded holes or nuts that are welded to the machine instead of threaded studs. The screw fastener  60  may include a sleeve  62 , or outer sleeve  62 , that is permanently attached to the guard  10  by welding the attachment surface  64  of the sleeve  62  to the guard  10 . The sleeve  62  may be welded to the guard  10  either by welding around the outer circumference of the sleeve  62  or providing weld nubs  65  on the attachment surface  64  of the sleeve  62  (as shown in  FIG. 8 ). When weld nubs  65  are provided, the sleeve  62  may be attached to the guard  10  by simultaneously pressing the sleeve  62  against the guard  10  and applying electrical current to the sleeve  62 . This causes the weld nubs  65  to melt into the surface of the guard  10  and welds the sleeve  62  and the guard  10  together. The guard  10  may be provided with a slotted opening  12  which may be aligned to a welded nut attached to a machine when the guard  10  is being installed onto the machine. The slotted opening  12  in the guard  10  typically has a width  14  that is approximately the same size of the threaded portion  90  of the screw  80  as shown in  FIG. 5  to minimize lateral movement between the guard  10  and the screw  80 . However, as shown in  FIG. 7 , the length  16  of the slotted opening  12  in the guard  10  is longer than the size of the threaded portion  90  of the screw  80  so that the screw  80  can move relative to the guard  10  along the slotted opening  12  when it is extended through the slotted opening  12 . 
         [0050]    The sleeve  62  also includes a slotted opening  66  that generally corresponds to the shape of the slotted opening  12  in the guard  10  so that the screw  80  can move along the length  16  of the slotted opening  12  in the guard  10 . However, the size of the slotted opening  66  in the sleeve  62  may be larger than the slotted opening  12  in the guard  10  to allow for the particular size of the inner sleeve  100  that is used. The slotted opening  66  in the sleeve  62  preferably has a width  68  that is approximately the same size as the second end  104  of the inner sleeve  100  to minimize lateral movement between the screw  80  and the sleeve  62 . The length  70  of the slotted opening  66  in the sleeve  62  may be larger than the size of the second end  104  of the inner sleeve  100  to allow movement of the screw  80  along the length of the slotted opening  66 . The sleeve  62  also includes an undercut space  72  below the slotted opening  66  that is larger in size than the slotted opening  66 . Preferably, the undercut space  72  extends the entire length from the slotted opening  66  in the sleeve  62  to the attachment surface  64 . The undercut space  72  receives a retaining member  106  of the inner sleeve  100 . Preferably, the width  74  and the length  76  of the undercut space  72  are both larger than the slotted opening  66  by the same amount to accommodate the larger size of the retaining member  106  both along the width  74  and the length  76  of the undercut space  72 . The width of the retaining member  106  and the contact surface  108  of the inner sleeve  100  may be approximately the same size as the width  74  of the undercut space  72  to minimize lateral movement of the inner sleeve  100 . The sleeve  62  further includes a second torque bearing surface  78  that is designed to engage with the first torque bearing surface  86 , or flange head, of the screw  80 . Thus, when the screw  80  is tightened onto a nut welded to a machine or other apparatus, compressive force is transmitted between the first and second torque bearing surfaces  86 ,  78  and through the sleeve body  62  to the attachment surface  64 . 
         [0051]    The screw fastener  60  also includes an inner sleeve  100  that is positioned within the sleeve  62 . The inner sleeve  100  has a first end  102  that is located toward the attachment surface  64  of the sleeve  62  and a second end  104  that is located away from the attachment surface  64  of the sleeve  62 . The retaining member  106  is larger than the second end  104  of the inner sleeve  100  and is preferably located at the first end  102  of the inner sleeve  100 . Thus, as shown, the retaining member  106  may be a flange  106  at the first end  102  of the inner sleeve  100  which forms a contact surface  108  that contacts the surface of the guard  10 . The retaining member  106  is also larger than the width  68  of the slotted opening  66  in the sleeve  62 . Therefore, the retaining member  106  prevents the inner sleeve  100  from being separated from the sleeve  62 . Preferably, the second end  104  of the inner sleeve  100  is smaller in size than the slotted opening  66  in the sleeve  62  so that the second end  104  extends at least partially through the slotted opening  66 . As shown in  FIGS. 6A-6C , the second end  104  may have flat sides  110  that engage the width  68  of the slotted opening  66  to prevent rotation of the inner sleeve  100  relative to the sleeve  62 . If the retaining member  106  is located at the first end  102  of the inner sleeve  100 , the second end  104  with flat sides  110  may extend the entire length to the retaining member  106  so that the inner sleeve  100  can slide through the slotted opening  66  until the retaining member  106  contacts the top  73  of the undercut space  72 . However, the retaining member  106  may also be located at an intermediate location. Thus, the first end  102  of the inner sleeve  100  may be an end portion  102  that forms an insert portion  102  extendable through the slotted opening  66  in the sleeve  62 . The inner sleeve  100  also includes inner threads  112  adjacent the first end  102  which are engageable with the external threads  90  of the screw  80 . An internal portion  114  of the inner sleeve  100  may extend from the inner threads  112  to the contact surface  108  of the inner sleeve  100 . Preferably, the internal portion  114  is larger in size than external threads  90  of the screw  80  so that the external threads  90  of the screw  80  do not engage the internal portion  114 . 
         [0052]    The screw  80  may be provided with numerous torque bearing surfaces  88 , but conventional hexagonal-shaped bearing surfaces  88  as shown in  FIG. 12  may be used. The screw  80  also includes conventional external threads  90  for engaging the internal threads of a welded nut. Preferably, the screw  80  includes a shaft portion  82  between the first torque bearing surface  86  and external threads  90  of the screw  80 . The shaft portion  82  may be smaller in size than the external threads  90  of the screw  80  and the inner threads  112  of the inner sleeve  100  so that the shaft portion  82  can slide through the inner threads  112  of the inner sleeve  100 . 
         [0053]    It is now apparent that the screw fastener  60  provides a screw assembly  60  in which the sleeve  62  and inner sleeve  100  may be permanently attached to a guard  10 . The screw fastener  60  provides a range of movement for the screw  80  that can correspond to a slotted opening  12  in the guard  10 . As described, the sleeve  62  may be welded to a guard  10  so that the position of the slotted opening  66  in the sleeve  62  mates with the slotted opening  12  in the guard  10 . This allows the screw  80  to move along the length of the slotted opening  12  in the guard  10 . Thus, the screw  80  can be threaded into a threaded hole or a welded machine nut by extending the screw  80  through the slotted opening  12  in the guard  10  regardless of where the welded machine nut is located along the length  16  of the slotted opening  12 . As a result, the guard  10  may be easily attached to the machine even if the guard  10  is not perfectly aligned with the machine. The screw  80  is also captured and retained onto the guard  10  to prevent the screw  80  from being dropped and/or lost when the guard  10  is removed from the machine. This makes it easier to reinstall the guard  10  and more likely that an operator will reinstall the guard  10  before using the machine. 
         [0054]    Unlike the nut fastener  20  described above, the screw  80  in the screw fastener  60  may be more easily removable from the sleeve  62  and the guard  10 . This may make assembly of the screw fastener  60  easier and less expensive during manufacturing and may make it easier for an operator to replace the screw  80  if it becomes damaged. To install the screw fastener  60 , the sleeve  62  is welded to the guard  10  as described above with the inner sleeve  100  captured within the sleeve  62 . The contact surface  108  of the inner sleeve  100  contacts the surface of the guard  10  to prevent the inner sleeve  100  from passing through the slotted opening  12  in the guard  10 . The retaining member  106  also prevents the inner sleeve  100  from fully passing through the slotted opening  66  in the sleeve  62 . After the sleeve  62  and inner sleeve  100  are permanently attached to the guard  10 , the threaded portion  90  of the screw  80  may be threaded through the inner threads  112  of the inner sleeve. The opposing flat sides  110  of the second end  104  of the inner sleeve  100  are particularly helpful when threading the screw  80  through the inner sleeve  100  because engagement between the flat sides  110  of the inner sleeve  100  and the slotted opening  66  in the sleeve  62  prevents the inner sleeve  100  from rotating during threading without needing to manually retain the inner sleeve  100 . If desired, the threaded portion  90  of the screw  80  may be threaded entirely through the inner threads  112  of the inner sleeve  100  so that the threaded portion  90  no longer engages the inner threads  112 . The screw  80  may now slide through the inner sleeve  100  since the inner threads  112  of the inner sleeve  100  need not engage the shaft portion  82  of the screw  80 , and the internal portion  114  of the inner sleeve  100  need not engage the threaded portion  90  of the screw  80 . Preferably, as shown in  FIG. 10 , the length of the threaded portion  90  of the screw  80  is approximately equal to or less than the length of the internal portion  114  of the inner sleeve  100  and the thickness of the guard  10 . In this arrangement, the end of the screw  80  will not extend all the way through the slotted opening  66  and the guard  10  when the threaded portion  90  of the screw  80  is fully threaded through the inner threads  112  of the inner sleeve  100 . Alternatively, if it is desirable to reduce the height of the screw fastener  60 , the length of the threaded portion  90  of the screw  80  may be within a 25% range of the combined length of the shaft portion  82  of the screw  80  and the second end  104  of the inner sleeve  100 . Because the total longitudinal movement of the screw  80  after it has been threaded through the inner threads  112  of the inner sleeve  100  is a combination of the sliding movement of the shaft portion  82  through the inner threads  112  and the sliding movement of the second end  104  through the slotted opening  66 , this arrangement may provide a smaller overall height of the screw faster  60 . Once the screw  80  has been fully threaded through the inner threads  112  of the inner sleeve  100 , the inner threads  112  act to capture the screw  80  to prevent it from being separated from the guard  10  unless the screw  80  is fully unscrewed from the inner sleeve  100 . At this stage, the screw  80  may slide relative to the inner sleeve  100 , and the inner sleeve  100  may slide relative to the sleeve  62  as desired to position the screw  80  for engagement with a threaded hole or a nut welded to the machine. 
         [0055]    While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein. Furthermore, the advantages described above are not necessarily the only advantages of the invention, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the invention.