Patent Publication Number: US-9422082-B2

Title: Container assembly and latch apparatus, and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a U.S. National filing under §371 of International Application No. PCT/US05/19352, with an international filing date of 3 Jun. 2005, and herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates generally to containers and components thereof, and specifically to apparatus and methods for engaging and disengaging various members of a container or similar apparatus to each other. Although the invention is primarily illustrated in connection with various components of a collapsible container, it has a wide range of potential applications and uses other than for containers. 
     Prior art bulk containers (especially those that are injection molded or blow-molded or otherwise formed from plastic) sometimes include an option of having one or more sidewalls that either (1) are solid, or (2) include multiple parts moveable with respect to each other. An example of the latter is a sidewall with a fold down access door (or “drop door”). The access door typically is hinged in an opening in the sidewall and can be secured in alignment with the sidewall (by latches or some other interlock). 
     Prior art bulk containers are sometimes provided in “collapsible” embodiments, so that the sidewalls can be folded down onto the base (or the container can otherwise be flattened), to take up less space when the container is not in use. For such collapsible containers, latches are sometimes used to engage sidewalls with other sidewalls, to help hold those sidewalls in a desired container configuration. 
     Examples of such containers and drop doors are described in pending U.S. patent application Ser. No. 10/256,631 (&#39;631), filed Sep. 27, 2002. The contents of that &#39;631 application are hereby incorporated by reference to, among other things, provide context and background for the present invention. 
     Prior to the present invention, container manufacturers who wanted to provide customers with a selection of sidewalls (ones with drop-doors as well as ones without) not only had to manufacture both types of sidewalls, but had to maintain an inventory of both types, sell both types, service and repair both types, etc. 
     In addition, the latches used in many prior art containers are susceptible to improper insertion or orientation within the sidewall and/or drop door panel. If a latch is inserted “backwards” or otherwise improperly, it may not sufficiently or securely engage the two adjacent parts, risking damage to the container, or to people and/or property around or in the container. 
     Moreover, many of the latches on a single container typically are different from each other, and must be positioned in a specific location on the container in order to work properly. This is even more true for drop door models, in which latches to engage the drop door to the sidewall are typically different from the latches used to engage the sidewalls to each other and/or to the rest of the container. This results in potential confusion, lost assembly time, and mistakes in assembly (drop door latches may be inserted into sidewall latch positions) both during manufacture and maintenance. It also requires that manufacturers and users (for manufacture, maintenance, and replacement purposes) carry a relatively complex and extensive inventory of latches and related parts. 
     Prior art latches typically do not provide an optimum balance between (a) ruggedness and security once assembled within the container, and (b) ease of assembly/replacement/maintenance as the need may arise. Among other approaches, prior art designs include interfering tabs behind which the latches must be forced during insertion. The tabs are intended to hold the latch from inadvertently dislodging, while also (at least theoretically) allowing replacement of the latch if necessary. In practice, removal of the latch from behind the tab can be significantly difficult or can even result in destroying the tab or sidewall/drop door itself. If the tab is broken or weakened by such removal (or otherwise is broken during use of the container), the latch typically can no longer be retained in the sidewall or drop door by the tab. Instead, unless the user decides to throw away the entire sidewall or drop door, the replacement latch must be affixed to the sidewall or drop door by some other means, such as by screws, glue, rivets, or the like. Such “permanent” affixation of the replacement latch not only takes more time than is desirable, but makes any subsequent replacement or maintenance on the latch even more difficult and time-consuming. 
     Further on that point, and specifically regarding collapsible containers, typical prior art latches are not reversible or otherwise usable for both sidewall latching and drop door latching. Such prior art approaches therefore require a separate latch for drop door latching and sidewall latching as those typically operate (pivot) in opposite directions (the drop door pivots outwardly, but the sidewall pivots inwardly). 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     It this therefore an object of the invention to provide a improved apparatus and method for joining pieces into an assembly, in a selective manner. By using a latch apparatus, hinged elements can function in a normal hinged manner with respect to each other, but by inserting a plug or similar element in place of the latch, the hinged elements can be locked to each other. The plug or locking/assembly aspect of the invention can be utilized in a wide variety of applications, including (by way of example) joining two or more pieces to each other even when there is not any hinged relationship between those pieces. 
     Another object of the invention is to provide improved latch apparatus and methods. Latches embodying the invention are useful in conjunction with the foregoing hinged elements and methods, or in other applications. In the preferred embodiments of the latch, the latch can be readily inserted and manipulated (to engage and disengage two things with each other); and readily removed and replaced/repaired. For embodiments such as described above; the latch preferably can be selectively replaced with a plug member of similar size and shape, to provide a relatively more permanent connection between the two things. Thus, and as described above and herein, one of the many applications in which the invention finds utility in providing the capability to readily convert collapsible containers or other bulk containers from open (drop door or access panel versions) to solid sidewalls, or vice versa. 
     In one embodiment, the invention provides for a molded bulk container consisting of a base and four sidewalls, where either a sidewall(s) with an access (drop) door or a solid sidewall can be assembled from the same molded components (an open side sidewall and a drop door). The desired configuration can be selected by inserting either door latches (for the access door version) or a latch plug (for the solid sidewall version), and preferably the assembly can be readily converted from either configuration to the other repeatedly, as the user desires or as circumstances demand. The open side sidewall and drop door thus can essentially form a solid sidewall by fixing the drop door in place by means of the plug. 
     An additional object of the invention is to reduce the number of molds or mold insert and/or eliminate the need to change molds or use mold inserts in the production or manufacturing process, when changing from solid to open side sidewalls (or vice versa). Among its many benefits, certain aspects of the invention permit the same molds (with no change or insert) and the pieces resulting from those mold to be used to make both (a) “solid” sidewalls and (b) access panel/drop door sidewalls. 
     An additional object of the invention is to provide a convertible container of the aforementioned character, in which the “solid wall” condition can be achieved without the presence of any hinges. Among other things, for customers and/or applications where no need for hinging is anticipated, the “solid” wall assembly can be provided without any hinges (thereby saving on costs, weight, etc. as compared to including a hinge in those “solid wall” embodiments). For such embodiments, the invention preferably includes interfering structures acting between the drop door and the sidewall, such structures engaging each other when inward and or outward forces are applied on the “solid wall” to increase the strength of the assembly. Among other things, these interfering structures can be similar to a tongue-and-groove construction, and can reduce the likelihood that such inward or outward forces might cause a gap between the bottom of the drop door and the confronting top of the sidewall (at the location where the hinge(s) normally would be) or might otherwise cause the sidewall/container to fail under such loading conditions. 
     By instead using certain embodiments of the invention, manufacturers need only fabricate and inventory (and sell, etc.) the components of the “drop door” version, because those components can be “pinned” to each other using the invention, to form a “solid” (non-drop-door) sidewall. The apparatus and methods of the invention also can simplify and improve the quality and efficiency of manufacture, installation, and removal of latches, such as those associated with separate, hinged and/or adjacent elements. 
     As indicated, and among other things, the invention can reduce the number of components and/or sub-assemblies needed for various applications. By way of example and not by way of limitation, the latches and/or plugs or other pin members can be used to selectively “fix” components to each other (such as parts of a container sidewall), effectively yielding a “solid” integral assembly from parts that otherwise could move with respect to each other. This can reduce overhead and costs tremendously. 
     Yet another object of the invention is to provide improved latches. By making latches interchangeable and/or keyed (rather than a custom latch for each location to be latched), the inventory/mold/maintenance costs/etc. are likewise reduced. 
     Other objects and advantages of the invention will be apparent from the following specification and the accompanying drawings, which are for the purpose of illustration only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a preferred embodiment of a collapsible container incorporating various aspects of the invention, with sidewalls and drop door in their erected positions, configured with the drop doors locked into place with plug members and the sidewalls erected and held in place with releasable latches; 
         FIG. 2  is a perspective view of a latch useful in connection with sidewall and/or drop door applications such as those shown in  FIG. 1 ; 
         FIG. 3  is an exploded view of the latch of  FIG. 2 ; 
         FIGS. 4( a )-( e )  show the latch of  FIG. 2  from different views (a—top view; b—side view; c—section view along line A-A of  FIG. 4( b ) ; d—end view; e—section view along line B-B of  FIG. 4( b ) ); 
         FIG. 5  highlights features of the inventive latch shown in  FIGS. 2-4 , as it can be used in connection with sidewall and/or drop door applications such as those shown in  FIG. 1  (further in that regard,  FIG. 1  shows plugs holding the drop door in a relatively fixed relationship to the sidewall, whereas  FIG. 5  illustrates an assembly having latches instead of plugs acting between the drop door and the sidewall); 
         FIG. 6( a )  is a section view taken along line B-B of  FIG. 5 ; 
         FIG. 6( b )  is an enlarged view of the selected portion C of  FIG. 5 ; 
         FIGS. 7-14  are perspective views of one of the many embodiments of the invention, illustrating one of the many sequences of movements that can be used to remove and install the latch of  FIG. 2  between a corresponding pocket or insertion location of a sidewall and a pocket of a related drop door; 
         FIGS. 15 ( 1 )-( 8 ) are similar to  FIGS. 7-14 , and illustrate one of the many uses and methods of assembly of the latch of  FIG. 2  with pockets of a sidewall and/or a drop door; 
         FIG. 16  is a perspective view of a plug-type apparatus useful for more permanently affixing two elements to each other, such as in connection with sidewall and/or drop door applications such as those shown in  FIG. 1  (and in place of the latch of  FIG. 2  in such applications); 
         FIG. 17( a )-( c )  shows the plug of  FIG. 16  from different views (a—bottom view; b—side view; c—end view); 
         FIGS. 18 ( 1 )-( 8 ) are similar to  FIGS. 15 ( 1 )-( 8 ), but show a preferred method for insertion and/or removal of the plug of  FIG. 16  into a pocket such as on a drop door (to “fix” the drop door to the rest of the sidewall); 
         FIG. 19  is similar to  FIG. 16 , but illustrates one of the many alternative embodiments of a plug member of the invention; 
         FIG. 20  shows the plug of  FIG. 19  from different views (a—bottom view; b—side view; c—end view); 
         FIG. 21  is similar to  FIG. 16 , but illustrates still another of the many alternative embodiments of a plug member of the invention; 
         FIG. 22  shows the plug of  FIG. 21  from different views (a—bottom view; b—side view; c—end view); 
         FIGS. 23( a )-( b )  show yet another of the many alternative embodiments of a latch member have a flexible appendage or leaf spring rather than the rear barrel sections and springs of the latch of  FIGS. 2-3 .  FIG. 23( a )  is a “top” perspective view;  FIG. 23( b )  is a “bottom” perspective view; 
         FIG. 24( a )  show a sectional view of the latch member of  FIGS. 23( a )-( b ) , taken along line  24 - 24  of  FIG. 23( b ) ; and 
         FIG. 24( b )  is similar to  FIG. 24( a ) , but shows the sectional elevation view of the latch member of  FIGS. 23( a )-( b ) , taken along line  24 - 24  of  FIG. 23( b ) . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Persons of ordinary skill in the art will understand that the components discussed herein can be fabricated from any of a wide variety of materials and processes. Preferably, the components are lightweight but suitably strong to withstand the loads and forces they may encounter during use. Among others, high/low pressure plastic injection molding, structural foam molding, or blow-molding can be readily utilized to form lightweight components or structures embodying the invention, for storage, transport, and handling of a wide variety of solid and liquid materials and things. Other fabrication methods include, by way of example, compression molding, rotational molding, gas/water assist molding, extrusion, or pultrusion. 
     For certain of the components described herein, materials such as nylon may be preferable (for certain latch and plug components), while alloy steel may be useful for other latch embodiments. Persons of ordinary skill in the art will understand that other manufacturing processes and materials may be readily utilized. 
     Additional strength can be introduced into many embodiments of the invention by using engineered grade resins, and/or fillers such as mineral or glass fillers. Preferably, embodiments of the invention are fabricated from strong, lightweight materials sufficient to support substantial loads and forces encountered in transporting and handling relatively heavy materials. For less demanding applications, thinner webs and/or different material may be sufficient. 
     Although the various embodiments are illustrated in association with drop doors and/or sidewalls for a collapsible container, persons of ordinary skill in the art will understand that the invention has broad utility. A wide range of components other than container components can be joined to each other using latch and plug (or other similar) components of the invention and, if desired, can be readily and repeatedly disengaged from each other (for repair, maintenance, improved access to an assembly&#39;s interior, reconfiguration from a hinged relationship to a fixed relationship or vice versa, or the like). 
     Turning now to  FIG. 1 , a preferred embodiment of the invention includes a collapsible container  270  having a base  275  and sidewalls  280 ( a )-( d ) pivotally attached to the base  275 . Any suitable means (including those shown generally in  FIGS. 1-36 ) can be used to hinge the sidewalls  280 ( a )-( d ) to the container  270 . One or more of the sidewalls  280 ( a )-( d ) may further include a drop door  285  pivotally attached, as described herein or otherwise. As illustrated,  FIG. 1  is configured with four drop doors locked into place with plug members, but with the sidewalls erected and held in their erected position with releasable latches (as more fully described herein). 
     The invention also preferably includes one or more latch members and/or plug members, to provide users with ease of assembly and maintenance, as well as flexibility of applications. As described herein, preferably, the plugs and latches are interchangeable with each other, so a user can selectively (a) install and use plugs to lock a drop door into a relatively fixed relationship with a sidewall or lock a sidewall or first element into a relatively fixed relationship with adjacent portions of a container or second element or (b) install and use latches to allow selective erection and/or engagement of those elements with each other via latching and hinging action, as previously described. 
     For embodiments of the invention involving a drop door within a collapsible bin or container sidewall, the relatively fixed relationship or “solid wall” assembly could have (1) no hinges (just using the plug members), (2) one or more hinges such as those described herein for the hinged version (although any such hinges would NOT be functioning so long as the plug was in place); or (3) other hinges or connecting elements (such as other plug members, not shown) located in or around the location at which the hinges are positioned for the hinged version. 
     Providing the “solid wall” condition without the presence of any hinges can be useful in many situations. Among other things, for customers and/or applications where no need for hinging is anticipated, providing the “solid” wall assembly without any hinges can save on costs, materials, assembly time, weight, etc. as compared to including a hinge in those “solid wall” embodiments. 
     Similar concepts apply for embodiments in which plugs hold the sidewalls to the rest of the container. The sidewall can have additional plugs, or no plugs or hinges at all, in place of the hinges shown in the drawings as connecting the sidewall to the base. 
     In addition to benefits to customers and users in the field (to be able to reconfigure a given container or other assembly from a hinged relationship into a “fixed” relationship), manufacturers can benefit by not having to purchase and maintain molds and inventory for as large a number of parts. By the preferred interchangeability of the latches, fewer “latch parts” have to be made and carried in inventory. The interchangeable plug concepts can even avoid the need for a separate “solid wall” mold and inventory (for those customers/users who do not need or want a drop door configuration, at least not all the time). 
     In that regard, one or more sidewalls  280 ( a )-( d ) and/or one or more drop doors  285  preferably includes at least one latch to permit engagement and disengagement between a sidewall  280 ( a )-( d ) and the container  270  and/or a drop door  285  and a sidewall  280 ( a )-( d ). As indicated above, certain embodiments of the invention also include at least one plug (preferably interchangeable with the latch, as explained herein) to securely and relatively “permanently” engage items to each other, such as a sidewall  280 ( a )-( d ) to the container  270  and/or a drop door  285  to a sidewall (a)-(d). 
     As shown generally in  FIG. 2  and in more detail in  FIGS. 3 and 4 ( a )-( e ), one of the many embodiments of the invention preferably includes a latch  290  to engage and disengage a first thing to a second thing. The first thing preferably has a pocket or similar area  295  (shown at least in  FIGS. 7-14 ) to removably receive the latch  290  and operatively position it for use as described herein. 
     Persons of ordinary skill in the art will understand that the latch components discussed herein can be fabricated from any of a wide variety of materials and processes. As with the other components discussed herein, the latch preferably are lightweight but suitably strong to withstand the loads and forces they may encounter during use. Among others, many of the latch components can be fabricated from nylon 6/6, while others (such as the actuating spring) preferably are of alloy steel or similar material. As indicated above, persons of ordinary skill in the art will understand that other manufacturing processes and materials may be readily utilized. 
     Additional strength can be introduced into many embodiments of the invention by using engineered grade resins, and/or fillers such as mineral or glass fillers. Preferably, embodiments of the invention are fabricated from strong, lightweight materials sufficient to support substantial loads and forces encountered in transporting and handling relatively heavy materials. As with other components discussed herein, for less demanding applications, thinner webs and/or different material may be sufficient. 
     Although the preferred embodiments are illustrated to include drop doors and/or sidewalls for a collapsible container, persons of ordinary skill in the art will understand that the invention has broad utility. A wide range of components other than container components can be joined to each other using the latches of the invention and, if desired, can be readily and repeatedly disassembled or otherwise disengaged from each other (for repair, maintenance, improved access to an assembly&#39;s interior, or the like). 
     The latch of the invention preferably is fabricated and configured to be removably received in a pocket on one of the things to be latched together. Although the latches described herein could be more permanently affixed to the thing or things to be latched (such as by gluing, welding, or the like), the preferred latching involves a relatively temporary physically fixed relationship between a latch (regardless of whether the latch is termed a first latch, a second latch, etc.) and a pocket (regardless of whether the pocket is termed a first pocket, a second pocket, etc.). In this regard, the pocket  295  and the latch  290  preferably are configured to be assembled so as to facilitate reliable engagement and disengagement of a sidewall  280  to a container  270 , and/or drop door  285  to a sidewall  280 . 
     However, as described below, the latch  290  also preferably is easily removed from the pocket  295  (for repair, replacement, or otherwise). Among other things, upon such removal of the latch  290  (or prior to its insertion), the pocket  295  is available to preferably removably receive a “fixed engagement” plug (regardless of whether the plug is termed a first plug, a second plug, etc.). In other words, the latch and plug preferably are sized and shaped to be interchangeable with each other, upon the selection of a user or customer. To further facilitate this interchangeability, the receiving pocket, the latch, and the plug members preferably are configured so that the latch or plug is held or retained in the pocket (against inadvertent or unintentional dislodgment) without any supplemental/additional hardware. The present invention&#39;s temporary selectable physical relationship between a latch  290  and a pocket  295 , or a plug and a pocket  295  contrasts with conventional latches that are intended to attach to objects in a more permanent physical relationship (such as by glue, bolts, rivets, screws, or like hardware). 
     As best illustrated in  FIG. 3 , the preferred latch  290  can be described conceptually as having two body portions  300  and  299  (or a plunger  300  and latch body  299 ) slidably joined to each other, with a compressed spring element or elements  310  and  370  forcing the two body portions to a normally extended position with respect to each other. 
     The body portions or first and second members (see below) preferably further include at least one pair of corresponding detent members (such as detents  365  and/or  380  on plunger  300 ) sized and configured to engage with a corresponding detent (such as track  385  on the latch body  299 ). Preferably, the detents are engaged or assembled with each other by forcing the plunger  300  into the latch body  299  (with the springs  310  and  370  between them) until the detent  380  pops into the slot  385 . The detent  380  can be formed with a sloped or cammed surface on its left side (when viewed in  FIG. 3 ), to facilitate the desired assembly but with a relatively vertical or tooth-shaped right end (again, when viewed in  FIG. 3 ) to preclude inadvertent or unintentional removal or dislodgment of the two body portions. When so assembled, the detent  380  can slide in slot  385  to permit the desired relative sliding motion between the plunger  300  and the latch body  299 . Thus, the assembled latch  290  preferably can be collapsed (preferably by hand pressure, pushing the two body portions toward each other and compressing the spring(s) for insertion or removal of the latch into an object or thing such as a sidewall or drop door. The detents can be used to limit the range of compression of the two body portions toward each other, but preferably at least prevent the two body portions from becoming disengaged unintentionally. 
     Alternatively, the latch  290  can be described as including a first member or tooth element  307 , a second member  300 , and a central body  305  joined to the first member  307  and movably connected to the second member  300 , with a third member  310  urging those two members away from each other. The third member  310 , typically a spring or similar device or element, is preferably housed or positioned within the central body  305  to force the second member  300  into engagement with the first thing, and the first member  307  into engagement with the second thing. Persons of ordinary skill in the art will understand that the latch, as well as the plugs and other elements of the invention) can be fabricated and provided in designs and assemblies that are different and/or more complex than those shown and described in detail herein. 
     The present invention also preferably includes a first pocket  295  on a first thing to removably receive a first latch assembly  290 . As shown in the drawings, the latch  290  assembled into the pocket  295  can be readily used for engaging and disengaging a first thing (such as a sidewall  280 ) to a second thing (such as a container  270 ). The embodiment in the drawing illustrates a plurality of such pockets  295 - 298 , to removably receive a corresponding plurality of latches  290 - 293 , to further facilitate engagement and disengagement between (a) the sidewall  280  and the container  270  or (b) a drop door  285  with the sidewall  280 . Persons of ordinary skill in the art will understand that, in addition, the invention could be described as having a first pocket  295  to removably receive a first latch  290  for engaging and disengaging a drop door  285  to a sidewall  280 , and preferably includes at least one more pocket  296 - 298  to receive at least one more latch  291 - 293  to further engage and disengage the drop door  285  to the sidewall  280  or the sidewall  280  to other parts of a container  270 . 
     As indicated above, movement of the central body  305  toward the second member  300  preferably compresses the third member  310  to permit engagement and disengagement of the first thing (sidewall  280 ) from the second thing (container  270 ), such as by one or more catch elements or teeth  307  being moved into and out of engagement with a corresponding opening on the second thing. Movement of the second member  300  toward the central body  305  preferably also compresses the third member  310  to permit the latch  290  to be inserted and/or removed from the pocket  295 . 
     The concepts of relative movement between the first member  307 , the second member  300 , the third member  310 , and the sidewall  280  and container  270  can also be described in reference to  FIGS. 5, 6 ( a ), and  6 ( b ). Those Figures show a sidewall  280  having a drop door  285 . The preferred sidewall  280  and drop door  285  each have a latch  290 ,  291  removably received into a corresponding pocket  295 ,  296 . In this arrangement, the latch on the right hand side of the figure (first latch  290 ) can be used to engage and disengage the sidewall  280  to another sidewall or other part of a container (not shown in  FIG. 5 , but such as end wall  280 ( b ) in  FIG. 1 ) and the second latch  291  (substantially the same as the first latch  290 ) can be used to engage and disengage the drop door  285  to the sidewall  280 . Other latches including a third latch  292  and fourth latch  293 , (substantially the same as the first latch  290  and second latch  291 ) are preferably included on the opposing end of the sidewall and drop door, respectively, as shown in  FIG. 5 , and operate in substantially the same way to engage and disengage those respective ends. Thus, in the embodiment of  FIG. 5 , the sidewall  280  is held in its erected position by two latches  290  and  292  (one at each end of the sidewall), and the drop door similarly is releasably engaged with the sidewall via two latches  291  and  293 . 
     Just as each latch (first  290 , second  291 , third  292 , and fourth  293 ) preferably is interchangeable (identical or substantially the same), so are each of the pockets  295 - 298  of the present invention. As explained below, however, the preferred latches and pockets also are “keyed” to help ensure that users install the latches in specific orientations, to provide additional benefits and ease of use. Persons of ordinary skill in the art will understand that this keying is not required and that many benefits of the invention can be realized with no keying (with every pocket being “identical” (capable of receiving an identical latch or plug regardless of its orientation) and a single standard reversible latch/plug configuration could be used in such embodiments. 
     Accordingly, even for the “keyed” embodiments, each latch  290 - 293  preferably is capable of being removably received by any of the pockets  295 - 298  (the keying instead ensuring that the latch is oriented properly, as explained herein). In other words, the latches preferably are interchangeable with each other, as well as will the plugs also described herein. 
     Said another way, in the preferred embodiment, any latch  290 - 293  may be received and removed from any pocket  295 - 298 , to facilitate ease of maintenance and assembly, as well as ease of conversion to a “fixed” state (a “uniform” plug preferably can be removably received by those same pockets  295 - 298 ). In addition, any “uniform” latch (such as illustrated as elements  290293 ) can be used to engage and disengage a sidewall  280  to a container  270 , or a drop door  285  to a sidewall  280 . 
     The “keying” of the latches is useful for certain applications such as the collapsible containers described herein because of the preferred folding pattern for those products. For many such containers, it is useful to have any drop doors fold outwardly (these doors typically provide access to the contents of the container while it is stacked with other similar erected containers, for example), but have the sidewalls collapse inwardly (so that they fold and stack over each other for ease of handling and shipment in their collapsed state). Among other things, this means that the flat side of the engaging teeth or projections  307  on the latch (the side of the teeth that contacts the other element, not the element that holds the latch within a pocket or similar area) needs to be oriented in one direction for drop doors (outwardly) and the other direction for sidewalls (inwardly). To ensure that the “uniform” single latch is inserted with the proper orientation, it can be keyed (and the receiving pockets similarly keyed), such as by the latch teeth and the pocket holes through which they extend being slightly off center (up or down, when the sidewall is erected). In that example of keying, by forming teeth holes slightly lower than center for the sidewall pockets (the pocket that holds latch  290  in  FIG. 6( b ) ) but slightly higher than center for the drop door pockets (the pocket that holds latch  291  in  FIG. 6( b ) ). Thus, for a given pair of adjacent latches (such as those illustrated in  FIGS. 6( a ) and 6( b ) ), the teeth holes in the pockets can prevent the latch from being inserted in the wrong orientation. Persons of ordinary skill in the art will understand that the other side of the door/sidewall combination (on the left side of  FIG. 5 , for example) might reverse the “off-center” positions of the sidewall and drop door pockets (so that the drop door teeth holes are lower than those on the sidewall) and that any suitable manner of keying, or combinations of ways of keying, may be utilized. 
     For ease of describing this aspect of the invention, latches, pockets, and plugs are each identified herein as being a first, a second, a third, etc., such element. However, persons of ordinary skill in the art will understand that these designations are not meant to limit, for example, a particular latch (first latch  290 ) to a particular pocket (first pocket  295 ), or even the number or location of those elements within a given application. Certain benefits of the invention can be realized, for example, for applications involving a single latch/plug/pocket. 
     The general principles of actuation and design of spring-actuated latches is known (in collapsible containers and other applications), and some of those concepts exist in the present invention as well (springs urge the engaging teeth outwardly, the teeth can automatically retract and reextend to engage between the elements, just by pushing the two elements together, etc.), although the present invention includes a number of features not present in existing latches. Returning now to  FIG. 6( b ) , the first latch  290  is shown in the condition of being held or removably received by a first pocket  295 . The first member  307  preferably includes or constitutes at least one tooth- or finger-like projection extending from the central body  305  that is inserted into a corresponding cavity or tooth-receiving opening  335  of the container  270 . The first member or members  307  preferably protrude from the cavity  335  and contacts the container  270  during engagement of the sidewall  280  to the container  270 . As shown in  FIG. 4( c ) , the preferably projection  307  is joined to the central body  305  such that movement of the central body  305  toward the second member  300  compresses the third member  310  and draws the projection  307  far enough away from the container  270  to disengage the projection  307  from the container  270 . However, the projection  307  preferably is not drawn far enough to disengage the projection  307  from the corresponding cavity  335 . 
     In the preferred embodiment, a user can operate the latch (once it is assembled into a receiving pocket) by moving the central body  305  toward the second member  310  from either side of the sidewall  280 . This useful bi-directional access is preferably facilitated by the provision of openings through the sidewall or drop door in which the latch is mounted. Each of the four latch pockets in  FIG. 5  preferably includes such an opening. For example, a window  340  (shown in sequential  FIGS. 7-14 ) is formed in the first pocket (the one in which no latch is yet assembled in  FIG. 7 ), and the latch  290  preferably includes a first recess  345  (shown in  FIG. 2 ) positioned on one side of the central body  305  and a second recess  350  positioned on the opposite side of the central body  305 . The recesses  345  and  350  preferably are separated from each other by a central web  351  and are at least approximately both the same size and shape (to facilitate the use of the latch in multiple orientations, for example, as described herein), although the gripping functionality provided by those recesses (described herein) can be provided in any suitable manner. The window  340  provides an opening for an end user to grasp one of the recesses  345 ,  350  and manually move the central body  305  toward the second member  300  to compress the spring  310 , facilitating engagement and disengagement of the sidewall  280  and the container  270 . 
     Preferably, the window  340  is large enough to allow the user to actuate and/or grasp the central body  305  (to permit the user to readily release the latched elements from each other). In this regard, preferably movement of the central body  305  toward the second member  300  is permitted. However, movement of the second body  300  toward the central body  305  preferably is prohibited or at least not as easy for a user to accomplish (thus helping to reduce the likelihood of inadvertent removal of the latch entirely from the pocket). Although the central body  305  may be actuated or moved from either side of the sidewall  280  (to engage and disengage the sidewall  280  from the container  270 ), in the preferred embodiment the first latch  290  may only be inserted into or removably received by the first pocket  295  from one side of the sidewall  280  (the outside, as the container is viewed when erected). 
     The preferred insertion and removal of the latch into a given pocket is also facilitated by collapsing the spring and other latch members toward each other, but preferably is not likely to occur during normal user actuation of the latch to engage or disengage the sidewalls, drop doors, or other components with each other. As shown in  FIG. 4( c ) , the second member  300  of the latch  290  is preferably positioned within a central body chamber  355  of the latch body  305 . Preferably, this sliding relationship (useful to permit the engagement/disengagement of the latched elements when a user presses latch body  305  toward second member  300 ) also permits a user to move the second member  300  toward the central body  305  a distance sufficient to allow the second member  300  to disengage from corresponding retaining structures/elements in the sidewall  280 . This permits the first latch  290  to be inserted into or removed from the first pocket  295  (or any similar latch to be inserted or removed in any similar pocket). Movement of second member  300  toward the central body  305  and/or the central body  305  toward the second member  300  preferably is limited (to avoid undo compression of the latch spring(s) or other potential failure of the latch) by the central body  305  contacting the end of the second member  300  housed within the central body chamber  355 . 
     As indicated above, and as further shown in  FIGS. 4( a )-( b ) , the first member  307  preferably is keyed (or positioned or offset) from one of the horizontal and/or vertical centerlines of the central body  305 . As also mentioned above, this allows the invention to help ensure against improper assembly/orientation of a latch in an application such as a collapsible container (such misorientation could have dangerous consequences, such as the container collapsing when loaded, etc.). In such “keyed” embodiments, the first latch  290  can be configured so that, to be inserted into (or “removably received by”) the first pocket  295 , the first member  307  requires insertion into the corresponding cavity  335  in a predetermined alignment. 
     In addition, the first member or tooth  307  preferably has an asymmetric shape, shown for example in  FIGS. 4( a ) and ( c ) , such that during engagement of the sidewall  280  to the container  270  a sloping or seating surface  299  on the first member  307  initially contacts the container  270 , forcing the central body  305  to move toward the second member  300 , collapsing the latch  290 , and permitting the first member  307  to engage the container  270  (whereupon the latch spring  310  forces the teeth  307  back out into interfering engagement with the container  270 ). 
     As shown in sequential  FIGS. 7-14 , the above described “keyed” attributes of one embodiment of the inventive latch provide for a first latch  290  that preferably (1) can be removably received by the first pocket  295  in a predetermined alignment to engage and disengage the sidewall  280  from the container  270  (see  FIG. 7 ), (2) can be disengaged from the first pocket  295  by moving the second member  300  toward the central body  305  (see  FIG. 8 ), (3) can be rotated to align the teeth or first members  307  with a corresponding cavity of a second pocket  296  (see  FIGS. 9-12 ), (4) can be removably received by the second pocket  296  by moving the second member  300  toward the central body  305  to permit the latch&#39;s teeth to be inserted into the drop door  285  prior to swinging the second member  300  into engagement with the drop door  285  (see  FIG. 13 ), and (5) the second member  300  is then swung into engagement with the drop door  285  and the latch is released by the person inserting same so that the distal ends  303  of the second member  300  engage corresponding detents or holes formed in the drop door, thereby helping retain the latch in its engaged relationship with the drop door and resulting in the latch  290  being “removably received” by the second pocket  296  (see  FIG. 14 ). 
     As explained above, in the collapsible container example of the drawings, the desired rotating of the first latch  290  (from its orientation in the first pocket  295 ) to align the first latch  290  with the second pocket  296 , means that the alignment of the first member  307  in the second pocket  296  differs from the alignment of the first member  307  in the first pocket  295 . For example, sequential  FIGS. 15 ( 1 )-( 8 ) show the preferred arrangement or direction of the asymmetric catch or teeth or first member  307  when removably received by the first pocket  295  (high and to the left) compared to being removably received by the second pocket  296  (relatively lower and to the right of the latch&#39;s centerline). 
     Accordingly, in one embodiment shown in  FIG. 1 , when erecting the sidewalls  280 ( a ) and  280 ( c ) to form the container  270 , the sidewall  280  is pulled in a direction away from the center of the container  270  such that the preferably sloped or curved shape  299  of the first member  307  is the first portion of the latch that contacts the end walls  280 ( b ) and  280 ( d ) of the container  270 . As noted above, this preferably forces the central body  305  to move toward the second member  300  and permits the first member  307  to engage the container  270 , thereby forming the container/sidewall assembly. Persons of ordinary skill in the art will understand that first member shapes other than the curve  299  shown in the figures may be utilized to urge or move the central body  305  toward the second member  300 . As mentioned above, to disengage the sidewall  280  from its latched relationship with the rest of the container  270  (the end wall  280 ( b ), for example), the user can move the latch&#39;s central body  305  toward the second member  300 . 
     As noted above, when engaging the drop door  285  to the sidewall  280 , the drop door  285  normally is pushed in a direction toward the center of the container  270  (rather than away from the container center, as with the sidewall), such that the preferably curved surface or shape  299  of the first member  307  makes the initial contact with the sidewall  280 . Given sufficient force on the drop door (applied by the user raising the drop door into its closed position) this preferably forces the latch&#39;s central body  305  to move toward the second member  300 , permitting the catch or first member  307  to engage the sidewall  280  (thereby closing the sidewall/drop door assembly into a planar position). Likewise, to disengage the drop door  285  from the sidewall  280 , the user moves the latch&#39;s central body  305  toward the second member  300  (thus retracting the catch or teeth from engagement with the sidewall  280 ). 
     Persons of ordinary skill in the art will understand that various other applications of the invention and arrangements of the pockets  295 - 298  and corresponding latches  290 - 293  (not shown) can allow latched/hinged elements such as the sidewall  280  and the drop door  285  to be closed in the same direction or in opposite directions (toward or away from the center of the container  270 ) relative to each other. 
     Returning to  FIG. 3 , the second member  300  preferably includes a first arm  360  operatively engaged with or even connected to the third member  310  and a second arm  365  operatively engaged with or even connected to a fourth member  370  (typically a spring or other force-generating/compressible/retractable device substantially the same as or identical to the spring or other force-generating/compressible/retractable device used as the third member  310 ). In one embodiment, the position and function of the third member  310  and fourth member  370  are 23 substantially the same with regard to the central body  305 . Accordingly, the fourth member  370  is positioned within the central body  305  to force the second arm  365  into engagement with the sidewall  280 , and the first member  299  into engagement with the container  270 . The first arm  360  and the second arm  365  are preferably connected by a bridge  375  to permit uniform/coordinated movement of the second member  300  toward the central body  305 . 
     As noted above, the bridge  375  also can ensure proper alignment of the detents  365  and/or  380  into the corresponding slots  385 , and those detents permit a restricted range of sliding motion between the plunger or second member  300  toward the central body  305  and restrict movement of the second member  300  away from the central body  305  (such as when the first latch  290  is removed from the first pocket  295  or is otherwise not engaged in a retaining pocket or similar structure). 
     One of the many alternative embodiments of the invention is illustrated in  FIGS. 23( a )-( b ), and 24( a )-( b ) . In those Figures, the retractable second member  300  of  FIG. 3  may be replaced with at least one flexible appendage(s)  700 ,  701  integrally molded with the central body  305 . The flexible appendages  700 ,  701  or “leaf springs” (similar to the preferred spring  310 ,  370  used in other embodiments) can be described as a force-generating/compressible/retractable device. 
     Persons skilled in the art will understand the basic material construction, device configuration and operation of the latch  705  shown in  FIGS. 23( a )-( b ) , minus at least the central body chambers  355  that houses the spring elements  310 ,  370 , is similar to the latch  290  shown in  FIGS. 2-4 . In other words; the latch  705  preferably includes a body portion  710 , a first member or tooth element  715  with associated “keying” attributes, and is removably received by a pocket  290293  to allow engagement and disengagement of a first thing to a second thing. 
     In this regard, insertion and removal of the latch  705  is preferably accomplished by placing the flexible appendages  700 ,  701  or “leaf spring” into a corresponding sidewall pocket, as described herein, flexing the flexible appendages sufficiently to allow the tooth elements  715  to be received into the sidewall pocket, and releasing the latch so that the tooth elements  715  are urged into their respective orifices within the sidewall and held in place by the material memory and/or flexing of the leaf springs  700 ,  701 . The latch  705  can now be gripped and flexed backward (to open a door or sidewall) and will be urged forward by the appendages  700 ,  701  (to latch or secure a door or sidewall). 
     In contrast to the multiple piece construction of the latch  290  embodiment shown in  FIGS. 2-4 , the latch  705  shown in  FIGS. 23( a )-( b )  preferably features a one-piece construction that typically reduces weight, complexity of operation, and production costs due to the reduced number of components when compared to the other latch embodiments described herein. The latch  705  preferably is made by injection molding or similar process, but can be fabricated by any of a wide range of suitable methods and from any suitably strong material. 
       FIGS. 24( a )-( b ) , show a perspective cut-away view and a cross-sectional view of the latch shown in  FIGS. 23( a )-( b ) . As shown in those figures, preferably the latch  705  includes a plurality of ribs or other elements forming molded compartments “A-F” as part of the single-piece latch assembly. Typically, these compartments “A-F” and associated compartment dividers, such as compartment divider  702  between compartments A and B, provide structural support or rigidity and/or gripping surfaces for the latch body. Persons of ordinary skill in the art will understand that the latch body and the addition or lack of any compartments will typically depend on, among other things, the intended application of the latch and any related stress or lack thereof the latch may experience. 
     The present invention also preferably may include one or more plug elements interchangeable with the latch elements described herein, to more permanently “fix” two elements to each other. Using the primary example of the attached drawings, a first single piece plug  390  can be used to securely engage the first thing (sidewall  280 ) to the second thing (container  270 ) or a drop door  285  to a sidewall  280 . Preferably, the first plug  390  can be selectively inserted into or be removably received by the first pocket  295  (or any similar plug can be inserted into any similar pocket/retention area), upon removal of the first latch  290  or if the pocket is otherwise empty. Thus, rather than requiring a variety of different plugs and/or latches, a plurality of similarly sized and shaped plugs and/or latches can be produced and/or used (or held in inventory for sales or maintenance, etc.) by manufacturers, distributors, users, etc. 
     As shown in  FIG. 16 , the first plug  390  preferably is formed as a unitary structure, although alternative embodiments (not shown) could be assembled from separate pieces. The plug preferably is sufficiently rigid to provide its desired “locking” function, but has sufficient flexibility to be installed and removed from various applications (such as pockets in collapsible container sidewalls and/or drop doors), as described herein. The plug preferably includes at least one catch or finger  395  (similar to the catch  299  of the latch  290 ) for engaging the container  270 . Although the body of the plug can be any suitable shape or configuration, it preferably has a similar size and shape as the preferred latch  290  (so that the plug can be readily interchanged with such latches in various applications). The body  405  of the plug can be described as preferably including a groove  410  (to permit some flexing of the body for aiding in inserting or removing the plug from certain applications). Alternatively, the preferred plug can be described as having a flange portion  400 , and a central base  405  joined to the finger  395  and connected to the flange  400  along a groove  410 . As noted herein, the groove  410  preferably helps facilitate the first plug  390  to be received by the first pocket, by permitting some flexing of the plug body  405 , with material memory of the plug preferably then returning the first plug  390  to its original non-deformed configuration to securely retain it in the pocket of the sidewall or drop door (such as drop door  275 ) and “fixedly” engage the sidewall  280  (or the other element to which the pocketed element is to be “fixed”). Persons of ordinary skill in the art will understand that the degree of any such “fixed” relationship of parts depends, among other things, on the degree of difficulty in removing the locking plug from such a “locked” relationship. In any case, the preferred plug preferably makes it more difficult to disengage the “locked” elements than does the latch  290 . 
     As shown in  FIGS. 17( a )-( b ) , similar to the catch or first member  307  of the first latch  290 , the finger(s)  395  of the first plug  390  are preferably keyed, or offset from one or both of the horizontal and vertical centerlines of the central base  405 , such that for the first plug  390  to be received by the first pocket  295  the first plug  390  requires insertion into the corresponding cavity  335  in a predetermined alignment. Among other things, this keying permits controlled orientation and insertion of the plug in certain applications (such as when the plug is formed with a relatively flat side  407  (see  FIGS. 1 and 16 ) so that surface  407  can form part of a generally flat interior of the sidewall, rather than having a recess such as recesses  345  and  350  on each side of the latch&#39;s central body  305 ). In other applications and embodiments not shown in the drawings, the plug can be formed without a generally flat surface  407 , such as with recesses or other shapes or configurations, and can include additional grooves  410  on either side of the plug body  405 , a central web between such recesses and/or grooves, or the like. Such alternative embodiments might permit, for example, a single plug configuration to be rotated and or used more universally within certain applications. 
     As shown in  FIGS. 18 ( 1 )-( 8 ), the catch or finger element  395  preferably is received by a corresponding cavity  335  of a pocket such as pocket  296 . The plug  390  preferably is aligned with the pocket  296  and removably received by the pocket  296 , by pushing the plug&#39;s central base  405  into the pocket. The relationship between the plug  390  and pocket  296  causes preferably is snug, to help prevent inadvertent dislodgment of the plug from the pocket. In part because of the preferred snug fit, the groove:  410  preferably is provided to enable the flange  400  to flex toward the central base  405 , for easier insertion and removal. In other words, flexing of the flange  400  toward the central base  405  is facilitated by the groove  410  or cutout area between the flange  400  and the central base  405 . After the plug  390  is positioned into the pocket  296 , the plug&#39;s material memory preferably returns the plug  390  to its original non-deformed configuration, which results in a secure interference fit engagement with the sidewall  280 . 
     In the embodiment just described, a single groove  410  is cut along one side the flange  400 . Accordingly, flexing of the flange  400  toward the central base  405  occurs on one side of the first plug  390 , and the beneficial flexing (to permit desired insertion/removal of the plug into or from a pocket) would not occur, or would not occur as readily, if a user attempted to insert the plug with the groove  410  facing toward the container (for the example illustrated in this portion of the drawings). As a consequence, unlike the substantially uniform construction of the first latch  290  (recesses  345  and  350  on each side of central body  305 , and second member  300  positioned substantially along the center of the central base  405  that allows the first latch to be rotated and oriented so that it can be received by and used in any pocket  295 - 298 ), the plug  390  as illustrated is preferably not interchangeable between a pocket  295  of the sidewall  280  and an adjacent pocket  296  of the drop door  285 . Among other things, rotation of the first plug  390  (such as the rotation illustrated in  FIGS. 7-14  for the latch  290 ) from its position in pocket  296  shown in  FIG. 18 ( 7 ) would inappropriately position the plug  390  for insertion of plug  390  within the adjacent pocket  295 , in part because it would not permit the necessary and/or desirable flexing of flange  400 . 
     Accordingly, in one embodiment of the present invention, two different plug designs are configured, one to be selectively used and removably received by pockets such as pocket  295  of the sidewall  280 , and another (such as that illustrated in  FIGS. 19 and 20 ) to be selectively used and removably received by the pockets such as pocket  296  of the drop door  285 . By comparing  FIGS. 16 and 17  to  FIGS. 19 and 20 , the reader can see that most elements and functions/methods of use of the two embodiments preferably are the same, with the exception being the position and orientation of the respective catches/teeth/fingers  395  and  595 . As shown in  FIG. 18 , the catches  595  are flipped upside down, further to the left and further up than the corresponding catches  395  in  FIG. 16 . This different orientation preferably allows the plug of  FIGS. 19-20  to be readily used in sidewall pocket  295 . 
     Persons of ordinary skill in the art will understand that the generally flat engaging/locking surfaces  396  of  FIGS. 17( a )  and  596  of  FIG. 20( a )  preferably are positioned to tightly contact the mating end wall surface of the collapsible container, much like the flat surface  286  of the catch  299  of  FIG. 4( a ) . However, surfaces  396  of  FIGS. 17( a )  and  596  of  FIG. 20( a )  also preferably have a slight taper (compared to the preferably more flat surface  286  on the latch  290 ), to further facilitate insertion of the relatively stiff plug into the pocket receptacle on the sidewall, drop door, or other thing. 
     Persons of ordinary skill in the art will understand that further alternative embodiments of the plug (such as a first plug  390  having a second groove (not shown) on the other side of the first plug  390  or a first plug  390  without a groove) could enable the first plug  390  to be removably received by any of the pockets  295 - 298 . 
     One of the many embodiments of a “direction-neutral” plug is shown in  FIGS. 21 and 22 , with one or more catch members or teeth/fingers  695  being centered on the face  698  of the plug (rather than being keyed via offsetting them horizontally or vertically on that face), and providing tapered surfaces  696  and  697  in opposing directions (rather than just a single direction) to facilitate insertion/seating/locking of the plug and the items to be locked to each other. 
     As further shown in  FIG. 18 ( 8 ), plugs such as the first plug  390  preferably are so snugly fit and fabricated from such stiff material that they normally can only be removed from the pocket by using a screw driver  501  or similar device to force flexing of the flange  400  toward the central base  405  thereby permitting the first plug  390  to be removed from the first pocket  295 . 
     As shown in  FIGS. 17( a ) and 17( c )  and the series in  FIG. 18 , the plug  390  is preferably retained in the pocket via the interfering fit of one or more detents or extensions  415 . These detents or extensions  415  preferably are sized and configured to engage the same holes or receptacles or detents formed in the drop door or sidewall that (as described above) receive distal ends  303  of the latch  290 &#39;s second member  300 . The insertion and removal of the first plug  390  into the first pocket  295  is preferably facilitated by tapering the extensions  415 , shown in  FIG. 17( a )  as tapered surface  416 . 
     Alternative embodiments of the first plug  390  including various catch or finger  395  shapes and orientations are shown in  FIGS. 19-22 , as described above. Among the many additional alternative embodiments (not shown), the plug could be fabricated with no groove  410  (making it less flexible at that location, and therefore possibly requiring thinner webs and flanges or less stiff material or a less snug fit to permit the desired insertion and/or removal), flat surfaces on both sides of the plug, or the like. 
     In some applications, it may be desirable to have a plug element or elements that can be locked as permanently as possible into the assembly, and that therefore may need little, if any, deformability. Instead, the plug or plugs could simply be forced into its locking position between the two “locked” elements (such as while it was still somewhat hot or had been softened by heating or similar treatment) and left there, with no intention of ever being able to remove it without destroying it or the locked elements or both. 
     As described above, a preferred embodiment of the invention includes a collapsible container  270  having a base  275  and sidewalls  280 ( a )-( d ) pivotally attached to the base  275 . Any suitable means can be used to hinge the sidewalls  280 ( a )-( d ) to the container  270 . One or more of the sidewalls  280 ( a )-( d ) may further include a drop door  285  pivotally attached, as also described herein. Additionally, one or more sidewalls  280 ( a )-( d ) and/or one or more drop doors  285  may include at least one latch to permit engagement and disengagement between a sidewall  280 ( a )-( d ) and the container  270  and/or a drop door  285  to a sidewall  280 ( a )-( d ). 
     The sidewall  280  may include one or more pockets such as a first pocket  295 , to removably receive a first latch  290  to engage and disengage the sidewall  280  from the rest of the container, and/or selectively and/or removably receive a first plug  390  (when the first latch  290  is not engaged in the pocket  295 ) to securely engage the sidewall  280  to the container  270 . Many of the components (such as the latches and plugs) preferably are interchangeable with each other, providing great flexibility to manufacturers, customers, and users with respect to production, inventory, and maintenance. 
     Similarly, the drop door  285  of the illustrated embodiment preferably includes one or more pockets such as a first pocket  291  substantially the same as the first pocket  290  of the sidewall  280 . The drop door pocket or pockets preferably also can removably receive a latch  290  to engage and disengage the drop door  285  to the sidewall  280 , and further preferably can selectively receive and retain a plug  390  to securely engage the drop door  285  to the sidewall  280 . In other words, in the preferred collapsible container embodiment, the latch  290  is interchangeable into any of a plurality of pockets on the drop door and/or sidewall  280 , so that a user, distributor, or manufacturer need only provide or stock one type of latch for the container (rather than a custom latch for each such pocket). Even though they are uniform (with respect to each other), that uniform latch design can include “keying” that, when combined with corresponding keying on the things to be latched (such as container sidewalls or drop doors or the like) can help ensure that the uniform latch is properly oriented and positioned in each respective pocket, to provide the desired secure and easy latching relationship between those components. Instead of latches, a plug  390  can alternatively (and preferably selectively) be placed into those pockets or retaining structures to securely and more “permanently” engage those components to each other (such as the sidewall  280  to the container  270  or the drop door within the sidewall. 
     The present invention also may be considered a conversion system, including a latch member  290  to permit hinged or other relatively moveable engagement and disengagement of a first thing to a second thing and a plug or locking member to hold the first and second thing in a more permanent relationship. Preferably, users can select (or “convert”) between the latch and plug to configure and reconfigure the assembly at any time and at virtually any location, into a wide range of selectable and useful states. Such states include, by way of example, a “locked” container that can not be readily collapsed, a collapsible container with effectively solid sidewalls (formed by locking drop doors into position within the sidewalls), and a fully operatively hinged collapsible container with one or more fully operatively hinged drop doors within the sidewall. 
     In such systems, the first thing preferably has a hinge apparatus  200  to permit rotation between the first thing and the second thing during engagement and disengagement of the first thing to the second thing, a pocket  295  to selectively and removably receive either a latch  290  (to facilitate the ready engagement and disengagement) or a plug  390  (to more permanently or securely engage the first thing to the second thing). The relationship of the first thing relative to the second thing transitions or converts from dynamic (when one or more latches  290  are used in the pocket or pockets) to relatively static (when the plug  390  is placed into the pocket or pockets. 
     Methods associated with the invention include, without limitation, (1) methods of assembling collapsible containers having latches and/or plugs of the foregoing character; (2) methods of converting the relationship of two or more things from a latched relationship (such as by using one or more latches of the aforementioned character) to a relatively more fixed relationship (such as by using one or more plugs of the aforementioned character); and (3) methods of manufacturing or inventorying or maintaining collapsible containers or similar multi-component assemblies by reducing the number of parts needed to provide or maintain both a (a) hinged item (such as a sidewall having a drop door hinged therein) and a (b) fixed, non-hinged item of similar configuration (such as a sidewall having a drop door “locked” therein to form a virtually solid sidewall that otherwise would have had to have been molded or provided by separate parts instead of locking the drop door into place). 
     The apparatus and methods of the invention have been described with some particularity, but the specific designs, constructions and steps disclosed are not to be taken as delimiting of the invention. Obvious modifications will make themselves apparent to those of ordinary skill in the art, all of which will not depart from the essence of the invention and all such changes and modifications are intended to be encompassed within the appended claims.