BACKGROUND OF THE INVENTION 
     This invention relates generally to a fitting for window coverings, in particular, a winder assembly for controlling the extension and retraction of a screen of a blind system. 
     PRIOR ART 
     A winder assembly refers to a user-operated blind component (or fitting) that is rotatable for, for example, extending and retracting a window covering such as a window blind. Such fittings typically have a drive mechanism that is rotatable about a spindle, and engages a cord (for example, a beaded cord or chain). Operation of the cord causes the drive mechanism to rotate about the spindle. For example, the cord may be pulled in one direction to rotate the fitting in a blind extending direction, and the cord may be pulled in an opposite direction to rotate the fitting in a blind retracting direction. 
     A cover is generally provided to prevent disengagement of the drive mechanism from the spindle, or the disengagement of the cord from the drive mechanism. In some winder assemblies, the cover is a separate component to the spindle, which may be engaged with the spindle in two or more positions. In one position, relative rotation between the spindle and cover may be prevented (e.g. a fixed or locked position), whereas in another position, the cover may be able to rotate to some degree relative to the spindle (e.g. a swivel position). The swivel position allows the angle of the cover to be changed relative to the rest of the winder assembly, and is favoured by users who wish to operate the cord while standing away from the window. 
     One problem with prior art winder assemblies of this type is that the spindle and the cover may accidentally disengage at undesired times—for example, when the spindle and cover are engaged in a fixed position, operation of the cord may occasionally disengage the cover from the spindle. The cover may remain disengaged for some time, which increases the possibility of the cord also becoming disengaged from the drive mechanism. In some cases, the cover may in due course re-engage with the spindle, but at an undesired position (e.g. the swivel position). 
     It is therefore desired to address the above issue, or to at least provide a useful alternative to existing winder fittings. 
     SUMMARY OF THE INVENTION 
     Accordingly, in a first aspect of the present invention, there is provided winder assembly for a window covering comprising:
         (a) a spindle comprising:
           (i) a head;   (ii) a shaft extending from the head; and   (iii) a location lug extending from the head in the direction of the shaft;   
           (b) a drive mechanism operable to control the extension and retraction of the window covering by rotation of the drive mechanism about the spindle; and   (c) a cover comprising:
           (i) an opening through which the shaft of the spindle passes, the cover releasably engaging the head of the spindle; and   (ii) at least one location aperture receiving the location lug to define at least one position of the spindle relative to the cover,   
               

     wherein the location lug has a pair of divergent walls extending outwardly from the head, and wherein the location aperture has a pair of divergent walls, at least one of that pair being engagable with at least one of the of the pair of divergent walls of the location lug. 
     The location aperture may be a fixed position aperture, wherein the pair of divergent walls of the location aperture engage the pair of divergent walls of the location lug. 
     In other embodiments, the location aperture may be a swivel position aperture, wherein the location lug is movable within the location aperture to define a path of rotational movement between the spindle and the cover. 
     Some embodiments of the present invention may comprise both a swivel position aperture and a fixed position aperture, allowing a user to select whether to allow rotation of the cover relative to the spindle. 
     The divergent walls may be straight side walls of the location lug, which are inclined or angled to diverge as they extend away from the head of the spindle. Alternatively, they may provide a curved or stepped divergence. 
     The location apertures may be radial extensions of the opening. Alternatively, they may be discrete apertures which are separated from the opening by a part of the cover. 
     The location lug may extend radially outward from the shaft of the spindle, such that it widens as it extends further from the shaft. 
     In a second aspect of the present invention, there is provided a spindle for a winder assembly comprising:
         (i) a head;   (ii) a shaft extending from the head; and   (iii) a location lug extending from the head in the direction of the shaft,       

     wherein the location lug has a pair of divergent walls extending outwardly from the head. 
     In a third aspect of the present invention, there is provided a cover for a winder assembly comprising:
         (i) an opening to receive a shaft of a spindle of the assembly; and   (ii) at least one location aperture to receive the location lug on the spindle to define at least one position of the spindle relative to the cover,       

     wherein the location aperture has a pair of divergent walls. 
     A detailed description of one or more embodiments of the invention is provided below, along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications and equivalents. 
     For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention. The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. 
     For the purposes of providing a clear description of the present invention, terms such as “front” and “rear” are used in the below descriptions. This terminology will be understood to be for illustrative purposes only, and does not limit the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Various embodiments/aspects of the invention will now be described with reference to the following drawings in which, 
         FIG. 1  is an exploded view of a winder assembly according to an embodiment of the present invention; 
         FIG. 2  is a rear perspective view of the winder assembly of  FIG. 1 , assembled. 
         FIG. 3  is a front view of a spindle and cover according to an embodiment of the present invention; 
         FIG. 4  is a transverse section view A-A of the spindle and cover in  FIG. 3 ; 
         FIG. 5  is an enlarged view of the area marked ‘B’ in  FIG. 4 ; 
         FIG. 6  is a front view of a cover according to an embodiment of the present invention; 
         FIG. 7  is a an enlarged section view C-C of the cover of  FIG. 6 ; 
         FIG. 8  is an enlarged section view D-D of the cover of  FIG. 6 ; 
         FIG. 9  is a perspective view of the spindle and cover of  FIG. 3 , with the spindle in a fixed position; 
         FIG. 10  is a perspective view of the spindle and cover of  FIG. 3 , with the spindle in a swivel position; and 
         FIG. 11  is a transverse longitudinal section view of the winder assembly of  FIG. 1 , assembled with the spindle in the fixed position. 
     
    
    
     DETAILED DESCRIPTION 
     A winder assembly  100 , as shown in  FIG. 1 , is suitable for use to raise or lower a roller blind. The winder assembly  100  includes a spindle  102  having a head  104  and a shaft  106 . A lug  108  extends from a rearward face of the head  104  in the direction of the shaft  106 , generally parallel to the axis of the shaft  106 . A cover  130  is mounted on the spindle  102  to releasably engage the head  104  of the spindle  102 , with the shaft  106  of the spindle  102  passing through an opening  132  in the cover  130 , so that the two parts snap together with the cover  130  releasably engaging the head  104  of the spindle  102 . The winder assembly  100  further includes a drive mechanism, comprising an inner core  140  and an outer drive element  150 , as well as a pair of clutch members  120 . The winder assembly  100  is held in its assembled state by screw  160  and end cap  170 , as shown in  FIG. 2 , although other fastening methods may be used in different embodiments of the invention. 
     In use, the winder assembly will typically be mounted to a supporting structure of some form—for example, a supporting frame or mounting bracket, with the spindle being fixed to that supporting structure. The outer drive element  150  has a plurality of fins around its outer surface, which are able to engage within a tube (not shown). A screen blind may be rolled around the tube. To raise or lower the blind, a cord (for example, a bead cord) is engaged with the inner core  140 , by teeth  142  around one end of the inner core  140 . This means that pulling of the cord rotates the drive mechanism about the spindle  102 , and is operable to raise or lower the blind. The clutch members  120  resist unwanted rotation of the outer drive element  150  about the spindle  102 . 
     In order to better show relevant features of the present invention,  FIGS. 3 to 10  show the spindle  102  and cover  130 , independently of the other components of the winder assembly  100 . The cover  130 , as best seen in  FIG. 6 , comprises an opening  132  through its centre, to receive the shaft  106  of the spindle  102 . It also comprises two additional location apertures (swivel position aperture  134 , and fixed position aperture  136 ) for engaging with the lug  108  on the spindle  102 , in two positions—a swivel position, and a fixed position. The location apertures are, in this embodiment, extended portions of the opening  132 , but in other embodiments they may be separated from the opening by a part of the body of the cover  130 . 
       FIGS. 4 ,  5  and  9  shows the spindle  102  and cover  130  engaged in the fixed position. In this position, the lug  108  engages within the fixed position aperture  136 . When in the fixed position, the spindle  102  and cover  130  are engaged such that they will not rotate relative to each other. 
     On the other hand, in the swivel position as shown in  FIG. 10 , the lug  108  is located within the swivel aperture  134  of the cover  130 . It will be appreciated that, to assemble the depicted winder assembly  100  in the swivel position, the orientation of the spindle  102  will be changed from the orientation shown in  FIG. 1 , so that the lug  108  is at the bottom of the head  104 , underneath the shaft  106 . Since the swivel aperture  134  is of the same depth as the lug  108 , but is much wider than the lug  108 , it allows rotation of the cover  130  relative to the spindle  102  —the lug  108  is moveable from one end of the swivel aperture  134  to the other through rotation of the cover  130 . This embodiment of the invention allows rotation of the cover  130  through almost 180 degrees in the swivel position, although other embodiments may allow a larger or smaller freedom of rotation. 
     The shape of the lug  108  facilitates an improved engagement between the lug  108  and the location apertures  134 ,  136 . As best seen in the detailed view of  FIG. 5 , the side walls of the lug  108  diverge as they extend outwardly from the head  104  of the spindle  102 . In this embodiment, the side walls of the lug  108  are simply straight walls which are angled with respect to the rearward face of the head  104 . 
       FIG. 5  also clearly shows how the side walls of the fixed position aperture  136  also diverge. In this embodiment, the side walls of the fixed position aperture are also straight side walls, at an angle to the main plane of the cover  130 , to match the angle of the side walls of the lug  108 . 
     If a twisting, rotational or other force is applied to disengage the cover  130  from the head  104  of the spindle  102  the corresponding angled side walls of the lug  108  and the fixed position aperture  136  will simply be driven into tighter engagement, due to the respective angled side walls. This will resist the disengagement force. Consequently, a winder assembly  100  in accordance with the present invention will be more difficult to accidentally disengage from the fixed position. 
     The dimensions of the fixed position aperture  136  will substantially match the dimensions of the lug  108 . However, typically some clearance will be provided, to allow the winder assembly  100  to be more easily assembled. In most cases, therefore, when a force is applied to disengage the cover  130  from the spindle  102  as described above, only one of the divergent side walls of the lug  108  will engage with a corresponding side wall of the fixed position aperture  136 . 
     However, there may be some embodiments where the lug  108  is tightly engaged or snap fit in the fixed position aperture  136 —for instance, if the lug  108  is formed of a resilient material. In these embodiments, with a tight fit between the lug  108  and fixed position aperture  136 , both side walls of the lug  108  may engage with the respective side walls of the fixed position aperture  136  at the same time. 
     The side walls of the swivel position aperture  134  are, in this embodiment, also angled to match the divergence of the side walls of the lug  108 . Accordingly, when the cover  130  is at either end of its freedom of rotation, the lug  108  will engage with one of the side walls of the swivel position aperture  134 . It will accordingly resist disengagement in a similar manner to that described above in relation to the fixed position aperture  136 , with the lug  108  engaging one of the side walls at either end of the swivel position aperture  134 , depending on the direction of twist or rotation applied by the force. 
     As can be seen from the figures, the lug  108  of this embodiment of the present invention also widens as it extends radially outward from the shaft  106  of the spindle  102 . The side walls of the location apertures  134 ,  136  match this radial widening. 
     It will be appreciated that the precise shape of the lug  108  may vary in different embodiments of the present invention. In particular, the side walls of the lug  108  may be curved (concave or convex) or stepped, rather than straight, and still provide improved resistance to disengagement of the spindle  102  from the cover  130 . The profile of the side walls of the location apertures  134 ,  136  would typically correspond to the profile of the side walls of the lug  108 . 
     The components of the winder assembly  100 , including the spindle  102  and cover  130 , may be formed from plastic, metal, or other material, and may be diecast or machined, depending on manufacturer or consumer preferences. 
     It will also be appreciated that the precise shape of the cover  130 , and especially its outer shape, may vary in different embodiments of the invention. The shape of the cover  130  depicted in the Figures is an example given for illustrative purposes only. 
     The word ‘comprising’ and forms of the word ‘comprising’ as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions. 
     Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention. 
     In this specification where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of the common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.
A winder assembly for controlling the extension or retraction of a window covering, for example a roller blind. The winder assembly includes a spindle having a head, a shaft extending from the head, and a location lug also extending from the head, in the direction of the shaft. The winder assembly further includes a drive mechanism operable to control the extension and retraction of the window covering by rotation of the drive mechanism about the spindle, and a spindle cover. The spindle cover itself includes an opening through which the shaft of the spindle passes, the cover releasably engaging the head of the spindle, and at least one location aperture receiving the location lug to define at least one position of the spindle relative to the cover.