Abstract:
A thread clamping device is described including a plurality of movable nut segments around a threaded rod, and spring members flexibly holding the segments against the rod. Smaller locking distances are shown to result by using at least one double-threaded segment as a component of the thread clamping device. Such a thread clamping device can advantageously be used as a component of a self-adjusting shrinkage compensation device, a coupler for threaded rods, hold-downs, among other uses.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention relates generally to the field of fastening devices and methods of use, and more particularly to threaded fasteners and thread clamping devices having improved locking characteristics in the ratcheting direction. 
         [0003]    2. Description of the Prior Art 
         [0004]    Wood is a major construction material in many places throughout the world. Wooden structures frequently use “tie-downs” to secure the wooden structure to its foundation, typically a concrete foundation or a concrete and block foundation. The function of tie-downs is thus to secure the wooden structure to its foundation in the presence of forces (perhaps substantial forces) tending to separate the structure from its foundation, such as high winds, seismic events or general shifting and settling of the surrounding earth. However, the wood typically used for construction often has considerable water content when initially installed and with time, the water evaporates and the wood dries out. In the process of drying out, the wood dimensionally shrinks. Approximately 4% shrinkage in the first year following construction of a wooden structure is not uncommon. 
         [0005]    This shrinkage commonly causes tie-downs to loosen, thereby making the structure more susceptible to damaging displacements in the presence of high winds, earthquakes among other external forces. Catastrophic damage may result. 
         [0006]    A common method for implementing a tie-down is by imbedding a vertical threaded rod into the concrete of the foundation at the location where the wooden structure is to be joined to the foundation. The threaded rod generally resides within the walls of a single or multilevel structure as it passes from the concrete foundation up through each floor of the structure. Each floor is typically attached to the threaded rod by a separate tie-down. The primary fastener presently used to implement a tie-down is a standard “hex” nut. 
         [0007]    If a standard nut is used, a space will typically develop under the standard nut and above the wood as the wood shrinks in dimension due to loss of water as described above. This space allows the tie-down (and structure) to move vertically when an overturning moment is applied to the structure as might occur, for example, during a seismic event, wind loading, among other circumstances. This motion of the structure with respect to the foundation, in turn, allows for deformation of the structural walls and may produce substantial damage that the tie-down is designed to prevent when functioning properly, that is when holding the structure securely in place on the foundation. Thus, a need exists in the art for a tie-down that is self-compensating, that is, a tie-down that maintains secure attachment of the structure to the foundation despite shrinkage of the wood. 
         [0008]    The International Codes Council (“ICC”) has recently adopted Acceptance Criteria (“AC”), AC316, that require Tension Controlled Shrinkage Compensation Devices (“TCSCD”) to meet certain performance criteria. Among these is a requirement that the deflection of the TCSCD under load is limited to 0.125 inch minus “looseness.” “Looseness” as used in this AC is defined as the distance the threaded rod must be moved in the locking direction relative to the TCD before the TCD segments lock to the rod. 
         [0009]    Receiving formal ICC approval for a device is an important commercial advantage in the US market. But ICC approval is based upon successfully passing independent performance tests and evaluations, providing strong evidence of the devices&#39; capabilities, even in those locations in which formal ICC approval is not called for. Thus, a need exists in the art for a TCD meeting ICC AC, and also demonstrating improved overall performance. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly and advantageously the present invention relates to thread clamping devices (“TCD”) and also to a TCD in combination with a bearing plate and various fasteners to form a self-adjusting shrinkage compensation device. Double-threaded nut segments are employed in connection with some TCD devices leading to a shorter locking distance for the TCD on the threaded rod and also improved strength, reliability, ease of use and/or other improved performance criteria. 
         [0011]    Some embodiments of the TCDS described herein employ a combination of ¼ thread phasing (four identical segments) and a double-thread configuration on one or more segments engaging a single-threaded rod. 
         [0012]    In view of the foregoing, in accordance with various embodiments of the present invention, a TCD is provided which may be advantageously configured pursuant to some embodiments of the present invention to move axially along a threaded rod in one direction without rotation (“ratcheting”), and further, will not move axially in the opposite direction without rotation. Indeed, in one embodiment, the TCD when combined with a bracket or bearing plate may become a “tie-down” for use in construction or for other purposes. 
         [0013]    A bearing plate to distribute the load and to prevent medium crushing is typically attached to the shrinking medium (such as wood) using any convenient attaching means such as traditional screws, nails, rivets, adhesives, among others. The bearing plate is typically sandwiched between the TCD and the shrinking medium. That is, the bearing plate is located between the TCD and the shrinking medium. For typical wooden construction, a threaded rod protrudes vertically from a concrete foundation and upwards through components of the wooden structure such as a wooden wall top plate for single level construction or floor plate for the above floors in multilevel construction. Thus, the TCD is “on” the rod above the bearing plate (where “on” denotes having the rod passing through the TCD and engaging therewith). In this manner, as shrinkage of the wood occurs, the screws typically attaching the TCD to the top plate or floor plate would pull the TCD downward with respect to the threaded rod. Each time the TCD moves a certain distance downward (the “locking distance,” typically at least one quarter (¼) thread), the TCD pursuant to some embodiments of the present invention has a structure that permits the TCD to internally ratchet and lock in place, thus preventing the TCD from moving upward with respect to the threaded rod (where the threaded rod itself cannot move as one end is buried in concrete during the construction process). Thus, the TCD maintains a tight tie-down despite shrinkage. 
         [0014]    In addition, some embodiments are specifically configured to use segments with a double thread to reduce or minimize the distance the TCD must move along the axis of the threaded rod before ratcheting occurs. Double-threaded segments can improve ratcheting performance whether the segments are identical or not, and also whether the segments have substantially planar or frusto-conical surfaces. 
         [0015]    Once ratcheting has occurred, some embodiments of include specific structures allowing the use of segments with double threads to reduce or minimize the linear distance the TCD is able to move without rotation in the opposite (non-ratcheting) direction before the TCD segments lock with the threaded rod. This performance characteristic of the TCD often called “looseness” or “looseness in the non-ratcheting direction.” 
         [0016]    A double-threaded segment engaging a single-threaded rod causes the thread ratcheting device, such as the TCD, to ratchet more often (that is, over a shorter linear distance along the rod) than would occur with a single-threaded segment engaging a single-threaded rod. 
         [0017]    Additionally, some embodiments relate to methods of attaching TCDs to commercially available “hold downs.” Hold downs attach to the medium subject so shrinkage (such as wood) and provide load distribution substantially similar to a bearing plate. Both mechanical and magnetic methods of TCD attachment to hold downs are described. 
         [0018]    Yet another advantage of TCDs in comparison with traditional hex nuts is that the TCD can typically successfully engage a damaged threaded rod, even in cases where a substantial portion of the threads of the rod have been deformed to the point where a standard hex nut will jam. 
         [0019]    An important performance criteria for the TCD, particularly in light of ICC AC316 discussed above, is to cause the locking distance to be sufficiently small such that the ICC AC is met. Thus, an objective of the present TCD is to provide a TCD having a small locking distance. 
         [0020]    Yet another objective of the present TCD to provide a device meeting ICC criteria and passing ICC tests. 
         [0021]    These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings. 
       BRIEF DESCRIPTION OF THE DRAWINGS 
       [0022]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings herein are schematic, not to scale and the relative dimensions of various elements in the drawings are not to scale. 
         [0023]    Some of the drawings depict threaded structures having internal threads, external threads or both. An artifact in the drawing program produces threads whose depiction in the figures may appear as lacking the true spiral structure of actual threads, although the thread profile is usually depicted properly. However, the threads are depicted herein for purposes of explaining various structures, embodiments and/or other features or uses in connection with the present invention, and the possible apparent absence of spirals in the depiction does not affect the description of the invention. 
     
    
     
         [0024]    The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0025]      FIG. 1  is a perspective view of a typical TCD on a threaded rod. 
           [0026]      FIG. 2  is a top view of a typical TCD without threaded rod. 
           [0027]      FIG. 3  is a first side view of a typical TCD. 
           [0028]      FIG. 4  is a second side view of a typical TCD. 
           [0029]      FIG. 5  is a top perspective three dimensional view of a TCD disassembled. 
           [0030]      FIG. 6  is a top perspective three dimensional view of a TCD disassembled. 
           [0031]      FIG. 7  is a top view of a typical end housing. 
           [0032]      FIG. 8  is a sectioned view of the end housing of  FIG. 7 . 
           [0033]      FIG. 9  is a three dimensional top perspective view of an end housing and two segments in different positions. 
           [0034]      FIG. 10  is a three dimensional top perspective view of an end housing and four segments. 
           [0035]      FIG. 11  is a three dimensional top perspective view of an end housing and four segments. 
           [0036]      FIG. 12  is a bottom perspective view of a TCD with top housing partially removed to reveal internal components. 
           [0037]      FIG. 13  is a top perspective view of four nut segments, coil spring and a threaded rod. 
           [0038]      FIG. 14  is an expanded outer perspective view of a single nut segment. 
           [0039]      FIG. 15  is an expanded inner perspective view of a single nut segment with a single thread. 
           [0040]      FIG. 16  is a close up inner perspective view of a single nut segment with a single thread. 
           [0041]      FIG. 17  is a cross-sectional view of a TCD and threaded rod depicting directions of segment motion. 
           [0042]      FIG. 18  is a cross-sectional view of a TCD and threaded rod depicting directions of segment motion with a double-threaded segment and single-threaded segment. 
           [0043]      FIG. 19  is a cross-sectional expanded view of a TCD and threaded rod depicting a double-threaded segment engaging a single-threaded rod. 
           [0044]      FIG. 20  is a perspective view of an assembly of TCD, mounting fasteners and bearing plate. 
           [0045]      FIG. 21  is an expanded view of a TCD and bearing plate installed on a structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    After considering the following description, those skilled in the art will clearly realize that the teachings of the invention can be readily utilized in the construction of thread clamping devices, self-adjusting shrinkage compensation devices, fasteners, among other structures and devices. 
         [0047]    We describe herein a thread clamping device (“TCD”) that engages with a threaded rod and can be moved without rotating in a ratcheting direction, but requires rotation and cannot be moved any significant distance by translation in the opposite non-ratcheting direction. The locking distance indicates the distance that the TCD moves before firmly engaging to the rod. It is shown that using double threads for at least a portion of the TCD structure leads to improved (shorter) locking distances. That is, a normally-threaded TCD has threads matching those of the rod with which it is to engage. A double-threaded TCD includes at least one segment having double threads (half the spacing) when measured in comparison with that of the rod (and the single-threaded segment(s), if any, of the TCD). Such a structure is shown to decrease the locking distance of the TCD but still engages with a standard-threaded rod. 
         [0048]    At least one double-threaded component causes a thread ratcheting device such as the TCD to ratchet more often for a given displacement along a threaded rod than a TCD with only single-threaded components, even though the rod along which ratcheting occurs has standard single threads. Simply explained, there are two basic components to a conventional thread system, a threaded rod and a threaded nut. In a standard system both rod and nut have the same number of threads per axial inch of length (defined as “threads per inch”). Also, in standard thread systems there is only one continuous thread. One way to verify a single-threaded structure is to observe the threaded rod end-on. In a single thread system there will only be one thread start at the end of the rod. A double thread system will have two thread starts at the end of the rod with each thread start being 180 degrees opposite of the other (that is, diametrically opposite across the rod diameter). In other words, a double-threaded structure (rod or nut) has two interleaved threads making their way along the structure, and performs quite differently from a single-threaded structure having twice as many threads per inch. 
         [0049]    A single-threaded rod will successfully engage a double-threaded nut so long as the helix angle of the (single) rod thread and (both) the nut threads are the same. The single rod thread will engage one or the other of the two (interleaved) nut threads, but not both at any one time. When a TCD having at least one double-threaded segment moves axially with respect to the single-threaded rod, the TCD will ratchet in approximately one-half the axial distance as would a TCD including only single-threaded segments. Since a double-threaded configuration has two threads in the same linear distance as the single thread in a single-threaded device, each of the double threads are one-half the size of a single thread of the same pitch and diameter. A possible disadvantage of engaging a double-threaded segment with a single-threaded rod is that there is less engagement area between the double threads and the single thread as there would be between two single threads of the same pitch and diameter, and therefore less force can be transmitted per thread. However, one may increase the total number of threads to be engaged (that is, use longer threaded segments engaging a longer distance along the rod) and therefore increase the thread engagement area to whatever is required. 
         [0050]      FIG. 1  is a schematic, perspective view of a typical TCD  222  engaged to a threaded rod  11  in accordance with some embodiments of the present invention.  FIGS. 2 ,  3  and  4  show a top view, a first side view and a second side view respectively of TCD  222 , omitting rod  11 . 
         [0051]      FIG. 5  depicts an exploded or disassembled view of TCD  222  including an end housing  210 , nut segments  214  supported by end housing  210 , and a top housing  212  engaging end housing  210  with one or more tabs  218 . Nut segments  214  are contained within top housing  212 . Surrounding nut segments  214  is coil spring  20 . For economy of language “nut segments” are also referred to as “segments” herein. 
         [0052]      FIG. 6  depicts an exploded or disassembled view of TCD  222  including an end housing  210 , nut segments  264  supported by end housing  210 , and a top housing  212  engaging end housing  210  with one or more tabs  218 . Nut segments are contained within top housing  212 . Surrounding nut segments  264  is coil spring  20 . Fastener holes are depicted as  220  in  FIGS. 2 ,  5  and  6 . 
         [0053]    Note:  214  and  264  both refer to nut segments. However, “ 214 ” is typically used herein to denote nut segments having a threaded surface containing only a single thread, that is, threaded in the same manner as the threaded rod  11 . “ 264 ” is typically used to denote a nut segment having a threaded surface with double threads. Various embodiments of the present invention can use single-threaded segments,  214 , or double-threaded segments  264  in various combinations and locations as discussed in detail elsewhere. In addition, for discussing structural features of the nut segments not related to the single- or double-threaded nature of the threaded surface, we will typically use  214  rather than the pedantic “ 214  and/or  264 ,” understanding thereby that nut segment features unrelated to the threaded surface apply equally to either type of segment. 
         [0054]      FIG. 20  depicts mounting fasteners  224  (or “fasteners”) passing through fastener holes  220  and plate fastener holes  228 , attaching TCD  222  to the shrinking medium  230  (typically wood) shown in  FIG. 20 . Upon installation of mounting fasteners  224 , bearing plate  226  is also attached in that bearing plate  226  is held securely between TCD  222  and the shrinking medium  230 . While nails are depicted in  FIG. 20  as the mounting fasteners  224 , any other fastener can be used, such as screws, rivets, among others. Also, it is usually convenient, but not required, that the multiple fasteners  224  used to attach TCD  222  to shrinking medium  230  be identical, in that circumstances may arise in practice calling for different fasteners  224  for different fastener holes  220 . 
         [0055]    While the top housing  212  (or “housing”) is shown with substantially cylindrical side surfaces, the housing  212  of the TCD  222  may include hexagonal, cubic, square and any other approximately tubular configuration capable of accommodating threaded rod  11 , and which is capable of containing the components of the TCD  222  as discussed in further detail below. 
         [0056]      FIG. 5  shows a typical complete TCD assembly  222  with the component parts exploded in a disassembled depiction. While four tabs  218  are depicted on end housing  210 , and four tab holes  216  in top housing  212  used to couple top housing  212  to end housing  210  (there is generally one tab hole  216  for each tab  218 ), fewer or more tabs  218  and tab holes  216  in pairs may be used depending upon the shape of TCD  222 . Coil spring  20  is shown above end housing  210 . The components depicted in  FIG. 5 , when assembled, comprise a typical TCD. 
         [0057]      FIG. 5  also shows slots  244  between end housing surfaces  246  and  248  in end housing  210 . There are, in this example, four slots  244 , four pairs of end housing surfaces  246 ,  248  arranged in a substantially equidistant polar array relative to central axis  8  (see  FIG. 8 ) in TCD  222 , all in end housing  210 . In a typical symmetrical TCD  222 , central axis  8  is coincident with the axis of the threaded rod  11 . End housing surfaces  246 ,  248  and slot  244  are defined as a feature set. Slots  244 , and end housing surfaces  246  and  248  advantageously form an angle of approximately 30 degrees relative to central axis  8 .  FIG. 5  also shows nut segment ribs  240 , segment spring groove  242 , right bearing surface  236  and left bearing surface  238 . There is one nut segment rib  240 , one segment spring groove  242 , one right bearing surface  236  and one left bearing surface  238  for each nut segment  214 . 
         [0058]    A nut segment assembly  250  includes a plurality of nut segments  214  in various configurations. For a concrete description, the present example depicts four nut segments in a nut segment assembly, but this is not an inherent limitation. More or less nut segments can be used as would be apparent to those skilled in the art. Also, various configurations of nut segment assemblies are described within the scope of the present invention. 
         [0059]      FIG. 7  is a top view of end housing  210 . Shown in top view are end housing surfaces  246  and  248  and slots  244 . 
         [0060]      FIG. 8  shows slot  244  and end housing surfaces  246  and  248  as substantially parallel and at substantially a 30 degree angle with respect to central axis  8 . Referring to  FIG. 5 , in an assembled configuration of nut segments in the end housing, right bearing surface  236  and bears against end housing surface  248  and left bearing surface  238  bears against end housing surface  246  for each of the four segments  214 . End housing surfaces  246  and  248  lie in a plane separated into two surfaces by slot  244 . Similarly, bearing surfaces (also called “segment surfaces”)  236  and  238  lie in a single plane separated by nut segment rib  240 . 
         [0061]      FIG. 9  is an upper perspective view of end housing  210 , depicting only two nut segments ( 214 A,  214 B) of the four in a full nut segment assembly in this example of a typical TCD. Segment  214 A is shown in an engaged position and segment  214 B is shown in an extreme disengaged position. It can also be observed that nut segment rib  240  resides substantially within slot  244 . All segment ribs  240  reside in their respective slot  244 . 
         [0062]      FIG. 12  is a three dimensional bottom perspective view of a typical TCD with a portion of end housing  210  removed and portions of top housing  212  removed. Also, one nut segment  214  has been removed for clarity revealing internal ramps  252 ,  253 , and center ribs  254 . Four ramps  252 , four ramps  253  and four center ribs  254  are depicted. However, there could be more or fewer depending on the relative sizes of the particular TCD under consideration and its internal components. The internal ramps  252  and  253 , and center ribs  254  comprise a portion of top housing  212  and have an orientation substantially parallel to respective end housing  210 , end housing surfaces  246  and  248 . The internal ramps  252  and  253  are configured in pairs. Each internal ramp pair engages a single nut segment  214  at that segment&#39;s left nut segment top surface  234  and right nut segment top surface  235 , as depicted in  FIG. 5 . For economy of language, we call  234  and  235  “segment top surfaces.” Each ramp pair ( 252 ,  253 ) is arranged in a quadrature polar array about axis  8 . (See  FIGS. 5 ,  9 ,  10 ,  13 ,  14 ,  15  and  17 ). Also shown are four tabs  218  extending outwardly from end housing  210 . 
         [0063]      FIG. 13  is a three dimensional perspective view of four nut segments  214  encircled by coil spring  20  comprising nut segment assembly  250  and engaged on threaded rod  11 . It is shown that, in the assembled configuration, coil spring  20  resides in segment spring groove  242  in each segment  214  respectively. The segments are shown in  FIG. 10  in the same position with respect to threaded rod  11  as they are depicted in  FIG. 13 . 
         [0064]      FIG. 14  is a three dimensional outer perspective view of one nut segment  214  of a typical nut segment assembly as would be used in a typical TCD  222  in accordance with some embodiments of the present invention. Shown in this illustration is segment spring groove  242 , left bearing surface  238 , right bearing surface  236  and nut segment rib  240 . 
         [0065]      FIG. 15  is a three dimensional inner perspective view of a nut segment (or “segment”)  214 , a component of the typical nut assembly  250  of TCD  222 . Also shown are left and right nut segment top surfaces  234  and  235  respectively, segment spring groove  242 , nut segment slot  232  and single segment thread  258 . 
         [0066]      FIG. 16  is a three dimensional inner perspective view of a nut segment  264  of nut assembly  250  of TCD  222 . Also shown are left and right nut segment top surfaces  234  and  235  respectively, segment spring groove  242 , nut segment slot  232  and a double segment thread  266 . 
         [0067]      FIG. 17  is a cross-sectional view of TCD  222  engaged with threaded rod  11  in accordance with some embodiments. Also shown in cross-section are any two opposing nut segments  214 , coil spring  20 , end housing  210  and top housing  212 . Also shown in  FIG. 17  are segment motion directions  260  and  262 . Other features shown are tabs  218  and tab holes  216 . 
         [0068]      FIG. 18  is a cross-sectional view of TCD  222  engaged with threaded rod  11  in accordance with some embodiments. Also shown in cross section are two opposing nut segments,  214  and  264 , coil spring  20 , end housing  210  and top housing  212 . Nut segments  214  and  264  may be in any combination in nut segment assembly  250 . Also shown are motion directions  260  and  262 . Other features shown are tabs  218  and tab holes  216 . 
         [0069]      FIG. 19  is a cross-sectional view of TCD  222  engaged with threaded rod  11  in accordance with some embodiments. Also shown in cross section is an enlarged view of segment  264  and its double-threaded surface  266  engaged with threaded rod  11  that has a standard single thread  268 . Other features shown are tabs  218  and tab holes  216 . 
         [0070]    In many applications, the nature of rod  11 , including its thread structure, is fixed by various building codes or other mandated standards. Thus, in such circumstances the nature of the threaded rod  11  is “given” and not subject to modification to come into conformity with the TCD to be used. However, as is clear in  FIG. 19  and from the general nature of double threads, double-threaded nut segment  264  readily engages with single-threaded rod  11 . 
         [0071]      FIG. 20  is a top perspective exploded view of TCD  222 , fasteners  224  and bearing plate  226 . Also shown is plate fastener hole  228  in bearing plate  226  above shrinking medium  230 . 
         [0072]      FIG. 21  is a top perspective view of TCD  222 , mounting fasteners  224  and bearing plate  226  shown installed to the shrinking medium  230  and engaged to threaded rod  11 . This combination of TCD  222 , mounting fasteners  224  and bearing plate  226  comprises a typical-self-adjusting shrinkage compensation device. 
         [0073]    In  FIG. 1 , TCD  222  may be configured to move along threaded rod  11  in one direction without rotation of TCD  222 , and to resist movement in the opposite direction without rotation. For the purposes of describing various embodiments of TCD  222 , the direction of motion whereby TCD moves along threaded rod  11  without rotation of the TCD shall be defined as the “ratcheting direction” and the opposite direction of motion as the non-ratcheting direction. However, even in the ratcheting direction, rotation of the TCD about the threaded rod will cause the TCD to move along the rod, but ratcheting in this direction without rotation is also possible. In particular, in accordance with some embodiments, TCD  222  may be configured to be engaged to threaded rod  11  such that a single downward hand movement of TCD  222  down the length of threaded rod  11  will correspondingly move TCD  222  in the ratcheting direction, to a desired position on threaded rod  11 . Once in place, an upward hand movement of TCD  222  along the length of threaded rod  11  will be met with an equal and opposite force such that TCD  222  will not move in the non-ratcheting direction. Rather, in order to move TCD  222  in the upward, non-ratcheting direction of threaded rod  11 , TCD  222  requires rotation along the threads of threaded rod  11 . The most common configuration with respect to TCD  222  engaged to a vertical threaded rod  11  is where (when viewed from above) a clockwise rotation of TCD  222  will advance TCD  222  downward with respect to threaded rod  11  and a counter-clock wise rotation of TCD  222  will advance TCD  222  upward with respect to threaded rod  11 . 
         [0074]    It should be noted that while the above description is given in terms of upward and downward hand movements of TCD  222  along the length of threaded rod  11 , the direction of the movements of TCD  222  may be arbitrary depending upon, for example, the position of threaded rod  11  on which TCD  222  is engaged. 
         [0075]    In some embodiments, TCD  222  will ratchet whenever TCD  222  is moved along threaded rod  11  a minimum of one-quarter (¼) of a thread pitch in the ratcheting direction. That is, when TCD  222  moves one-quarter of a thread pitch one of the segment pairs will ratchet such that, if forces try to move the nut assembly in the opposite non-ratcheting direction, a minimum of one nut segment will lock up and prevent motion in the opposite, non-ratcheting direction with respect to threaded rod  11 . One configuration implementing ¼ thread ratcheting includes four identical segments  214  arranged in all four segment positions as depicted, for example in assembly  250  shown in  FIG. 5 . 
         [0076]    In other embodiments, TCD  222  ratchets whenever TCD  222  is moved along threaded rod  11  a minimum of one-eighth (⅛) of a thread pitch in the ratcheting direction. That is, when TCD  222  moves one-eighth of a thread pitch, one of the segment pairs will ratchet such that, if forces try to move the nut assembly in the opposite non-ratcheting direction, a minimum of one nut segment will lock up and prevent motion in the opposite direction with respect to threaded rod  11 . To implement ⅛ thread ratcheting four identical segments  264  are arranged in all four positions. 
         [0077]    In particular with respect to  FIG. 12 ,  FIG. 13 ,  FIG. 14 ,  FIG. 15  and  FIG. 17 , each of the four segments are driven upwards and outward at an angle of about 30 degrees relative to central axis  8  as a result of nut segment top surfaces  234  and  235  contacting internal ramps  252  and  253  ( FIG. 12 ) as threaded rod  11  is pushed upward, for example, by seismic movement or winds that cause building over-turning moments. Over-turning moments cause a structure to move up and down with respect to its foundation. In this case, with enough linear movement  260  and/or movement  262  ( FIG. 17 ), segments  214  will completely disengage threaded from the threads of threaded rod  11 , and re-engage when the next thread of rod  11  moves into position to allow the four segments  214  to move toward the center of rod  11  and re-engage the threads of threaded rod  11 . 
         [0078]    On the other hand, if the forces reverse in direction and threaded rod  11  is driven down (or TCD  222  is driven up), nut segments  214  will be driven toward threaded rod  11 , and the threads will stay engaged (as long as the downward force exists) because of the inward radial force pushing segments  214  toward threaded rod  11 . The inward radial force is generated by end housing surfaces  246  and  248  of end housing  210  contacting surfaces  238  and  236  respectively of segment ( FIGS. 5 ,  7 ,  8 ). Also to be considered is the outward radial force caused by the interaction of the thread flanks of rod  11  against segment thread&#39;s flank (for example,  258 A,  258 B of  FIG. 15 ). The inward radial force relative to axis  8  on segments  214  overcomes the outward radial force on segments  214  as long as the included angle between thread flanks ( 258 A and  258 B in  FIG. 15 ) remains substantially 60 degrees (which is the standard flank angle for American Standard and Metric threads), and the angle of end housing surfaces  246 ,  248 , and bearing surfaces  238  and  236  remain substantially 30 degrees relative to axis  8 , and the reversing forces are in effect. The resultant inward forward force keeps the segments  214  engaged with threaded rod  11 . 
         [0079]    Moreover, in some embodiments the material used for nut segments  214  may have a yield point greater than or equal to that of the material of threaded rod  11 . Even when the yield points are reasonably close between the materials for threaded rod  11  and segments  214 , and one segment  214  begins plastic deformation, as soon as threaded rod  11  moves, other segments  214  will start to engage threaded rod  11  to overcome the strength of threaded rod  11 . 
         [0080]    Alternatively, the material used for nut segments  214  may have a yield point substantially lower than that of threaded rod  11 , in which case threaded rod  11  will still fail (i.e., give way or break off) before TCD  222  is compromised if there is sufficient length of thread engagement. 
         [0081]    Moreover, coil spring  20  in some embodiments is configured to have sufficient tension to cause nut segments  214  to close around threaded rod  11  even in the case where the gravitational force is pulling nut segments  214  away from threaded rod  11  (for example, in the case where TCD  222  is inverted). Indeed, if nut segments  214  are not driven toward threaded rod  11  center by the force exerted by the coil spring, nut segments  214 , may move to the outside of the wall of top housing  212  and remain in that position resulting in TCD  222  not engaging with threaded rod  11 . 
         [0082]    Referring to  FIG. 17 , the segment motion directions  260  and  262  illustrate the manner in which nut segments  214  are configured to move when TCD  222  moves in the ratcheting direction with respect to threaded rod  11 . 
         [0083]    Referring to segments  214 , the engagement of nut segment ribs  240  and slots  244  provide linear guidance and transfer torque to nut segments  214 . The nut segment ribs  240  and slots  244  are configured to engage one another. Nut segment ribs  240  appear on segments  214 . The matching slots  244  appear on end housing  210 . When torque is applied to end housing  210  this torque is transmitted to segments  214  through slots  244  engaging nut segment ribs  240 . Additionally, the nut segment ribs and slots also guide the radial motion engagement of TCD  222  to threaded rod  11 . Torque may be applied to end housing  210  through top housing  212 . 
         [0084]    Referring to  FIGS. 3 ,  4 ,  5 ,  7 ,  8 ,  9 ,  10 ,  12  and  17 , torque is transmitted from the top housing  212  to end housing  210  through tab holes  216  on top housing  212  engaging tabs  218  on end housing  210 . Torque is also transmitted directly from the top housing to nut segments by center rib  254  ( FIG. 12 ) engaging nut segment slot  232 . The tab holes  216  and tabs  218  also perform a fastening function and facilitate automatic assembly of the top housing  212  to the end housing  210 . During final assembly the top housing tab holes  216  are aligned over the end housing tabs  218  and then the top housing  212  is pushed down over the end housing  210 . The tabs  218  force the wall of top housing  210  outward over the tabs  218  until the downward motion of the top housing  210  allows the tabs  218  to snap into the tab holes  216 . The top housing  212  now cannot be removed from the end housing  210  without damage to the top housing  212 . This accomplishes the final assembly of the TCD  222  without the use of fasteners. 
         [0085]    Referring to  FIGS. 8 and 12 , there is lead-in  256 , advantageously conical in shape although other shapes are not excluded, which guides the TCD  222  over the threaded rod  11  upon initial engagement of TCD  222  to the end of threaded rod  11 . The conical lead-in  256  causes the installation of TCD  222  to be quick and easy as the conical lead-in  256  guides the end of threaded rod  11  to the center of TCD  222  and to the bottom of nut segments  214 . The nut segments  214  then move as depicted in to  FIG. 17  as described in more detail elsewhere. 
         [0086]    With respect to top housing  212 , it should be noted that some embodiments of this invention require torque to be applied to housing  212  in order to tighten or loosen TCD  222  with respect to threaded rod  11 . Application of torque is typically applied with a wrench, pliers or other device engaging exterior flats of a housing equivalent in function to top housing  212  but including exterior flat surfaces to facilitate gripping. 
         [0087]    It should be clearly understood that the threads of the TCD&#39;s nut segments may, but need not, be identical from segment to segment. Indeed, completely identical thread structures in adjacent segments (single- or double-threaded) will have the proper phasing to form a single continuous thread around the interior of nut segment assembly,  250 , only if the segments are vertically displaced with respect to each other. But such configurations nevertheless perfectly acceptable configuration in some embodiments. Other acceptable configurations include distinct nut segments having proper thread phasing to form a single continuous internal thread. Various combinations of single- and double-threaded segments are also acceptable in some embodiments, recognizing that at least one double-threaded segment is needed to achieve a shorter locking distance. Indeed, some advantages can be expected to result from having two different thread structures in the same device. 
         [0088]    To illustrate the potential advantages of employing different thread structures, we consider a nut segment assembly having four segments, as in  250 . However, this is not an essential limitation and other numbers of nut segments can be employed and still achieve the advantages described herein. 
         [0089]    For example, in the case of a nut segment assembly having four segments with two thread types (“TT”), TT-A and TT-B, the segments having the same thread types are located diametrically opposite across central axis  8 , or in other words, circumferentially alternating A-B-A-B, denoted as TCD(ABAB). For example, if TT-A were an American National Standard for Unified Screw Threads, and TT-B were from the International Metric System, then TCD(ABAB) could successfully be used with either of two threaded rods, one having TT-A or another having TT-B so long as the diameters of the two rods were sufficiently similar so both would accommodate TCD(ABAB), typically within about 25% of having the same diameter. 
         [0090]    In addition, TT-A could be a right-hand thread type (standard configuration), while TT-B could be a left-hand thread type (non-standard configuration). This embodiment of TCD(ABAB) would successfully engage either a right-handed-threaded rod (TT-A) as well as a left-handed-threaded rod (TT-B) with two of the four nut segments engaging each type of rod. Since two of the TCD(ABAB) nut segments can be configured to be stronger than the engaged rod, maximum usable strength can be present in this form of TCD(ABAB) even with two unengaged segments. 
         [0091]    In addition, a functioning TCD can be constructed when TT-A is a coarse thread (such as UNC-Unified National Coarse), while TT-B is a fine thread (such as UNF-Unified National Fine). Numerous other configurations of thread types and arrangements of nut segments within the nut segment assembly, following the teachings presented herein, will be apparent to those having ordinary skills in the art. 
         [0092]    Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific embodiments, it should be understood that the invention should not be unduly limited to such specific embodiments. 
         [0093]    Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.