Abstract:
An adjustable-length pole ( 10 ) for sticks, having an outer tube ( 12 ) and an inner tube ( 11 ) that can be inserted telescope-like into the outer tube ( 12 ) for adjusting the length of the tube, and having a spreading device ( 15 ) that is supported at the insertion end of the inner tube ( 11 ), the spreading device being able to clamp the inner tube ( 11 ) axially in the outer tube ( 12 ) and having a spreading element ( 16 ) that can be radially pressed apart and that is furnished with an inner cone ( 27 ), an interior element ( 17 ) that is provided with a reverse-oriented outer cone ( 22 ) and that is accommodated in the spreading element ( 16 ) so as to be axially movable, and an adjusting screw ( 18 ) that is axially oriented and is supported in a rotationally fixed manner on the inner tube ( 11 ), the adjusting screw having an operational connection to an internally threaded bore ( 21 ) in the interior element ( 17 ). So that an adjustable-length tube of this type responds to impact-like axial stresses by continuing to clamp rather than sliding or giving way, provision is made that the inner cone ( 27 ) of the spreading element ( 16 ) is situated such that it opens in the direction of the inner tube ( 11 ), and the spreading element ( 16 ) is supported between an inner limit stop ( 28 ) on the inner tube ( 11 ) and an exterior limit stop ( 26 ) on the free end of the adjusting screw ( 18 ) so as to be axially movable within narrow limits.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation-in-Part of application Ser. No. 10/511,294 filed Oct. 15, 2004, now U.S. Pat. No. 7,726,898. The entire disclosure of the prior application, application Ser. No. 10/511,294 is considered part of the disclosure of the accompanying continuation-in-part application and is hereby incorporated by reference. 
    
    
     Application Ser. No. 10/511,294 is the national stage of PCT/EP03/03805 filed on Apr. 11, 2003 and also claims Paris Convention priority of DE 202 07 54.0 filed on May 8, 2002. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an adjustable-length stick or adjustable-length pole, having at least a first and a second tube that telescope and are joined by a spreading element, of the type used in hiking poles or ski poles. 
     In an adjustable-length stick such as is known from DE 297 06 849 U1, the spreading element is provided with a tapering inner cone with an apex oriented towards an inner tube, whereas the corresponding interior element that is provided with the outer cone is displaced towards the inner tube by an adjusting screw so that the spreading device can grab hold. In this manner, although the result is a relatively parallel clamping over the entire axial length of the spreading element, nevertheless it has been found that in response to impact-like stresses on the stick tip from the handle-side of the adjustable-length stick, an axial displacement of the outer tube with respect to the inner tube cannot always be avoided and especially not when, in a twisting motion used to expand the spreading element, insufficient force has been applied for purposes of clamping. 
     Furthermore, from DE 297 08 829 U1, an adjustable-length stick is known, in which an interior element that is provided with an outer cone is formed by a forward free end of an adjusting screw, and a spreading element that is provided with an inner cone is moved axially on the adjusting screw. In this context, although the inner cone of the spreading element is opened towards the inner tube, nevertheless the same aforementioned disadvantages arise here if the spreading element is axially fixed in the spread-apart state. In this case as well, a relative motion between the outer tube and the spreading element can occur. 
     The objective of the present invention is to create an adjustable-length stick, especially for poles, of the species cited above, which, in response to impact-like axial stresses, continues to clamp rather than slide or give way. 
     SUMMARY OF THE INVENTION 
     The features of the present invention combine to achieve this objective in an adjustable-length pole, especially for one having telescoping tubes, of the aforementioned kind. 
     As a result of the features according to the present invention, it is achieved that in response to an aforementioned impact-like stress, the holding force between the spreading element, or inner tube, and the outer tube is increased, because as a result of the relative axial movability of the interior element and the spreading element, the interior element is able to penetrate further into the inner cone of the spreading element. Even in the case of a telescope mechanism where a spreading element is tightened using too little torque, the result is essentially a further spreading, which in turn reinforces the clamping force in the direction of the stress, so that even in these cases a displacement or a relative motion is prevented. 
     In a preferred embodiment of the invention, the spreading element is configured in a pot-like fashion, with a pot base being penetrated by a free end area of said adjusting screw, facing away from said inner tube. 
     In another preferred embodiment, the spreading element comprises a cylindrical shoulder having a smaller exterior diameter and facing said inner tube, with the shoulder being axially guided at one area of said end of said inner tube. 
     In both these embodiments, a jam-free guiding of the spreading element within the given axial movability is provided. 
     In an advantageous embodiment with regard to an outer limit stop for the spreading element, the outer limit stop is formed by a cap that is axially secured at the free end of the adjusting screw after the spreading element has been set in place. The assembly of the spreading element thereby takes place before attachment of the outer limit stop. 
     In an alternative embodiment of the invention, the exterior limit stop is formed by a head that is moulded onto the free end of the adjusting screw, and the spreading element has a peripheral slot that extends along an entire axial length thereof. With the stop already provided, the spreading element is configured such that it can be radially placed onto the adjusting screw and the interior element. 
     In one advantageous embodiment of the inner limit stop, the spreading device has a plug that accommodates the adjusting screw in an axial and rotationally fixed manner, the plug being supported axially and in a rotationally fixed manner in the inner tube and defining the inner limit stop. The plug has an axially protruding guide member cooperating with the cylindrical shoulder of the spreading element. 
     In another exemplary embodiment of the invention, the interior element has one or more radially protruding fins, which are guided in axial slots of the spreading element. A rotationally fixed axial movability of the interior element with respect to the spreading element is thereby achieved. 
     In a further exemplary embodiment of the invention, the adjustable-length pole comprises: at least one outer tube; an inner tube structured and dimensioned for insertion into the outer tube in a telescoping fashion for adjusting a length of the pole; a first limit stop disposed at an end of the inner tube; an adjusting screw being axially oriented within the outer tube, non-rotatable with respect to the inner tube and supported in a fixed manner on the end of the inner tube; a second limit stop disposed on a free end of the adjusting screw; a radially spreadable element with a non-threaded bore and with only one single inner cone, the inner cone opening towards the end of the inner tube, wherein the radially spreadable element is disposed with its axial length between the first limit stop disposed at the end of the inner tube and the second limit stop disposed on the free end of the adjusting screw, and wherein the distance between the first and second limit stops is larger than the axial length of the radially spreadable element by a gap distance, such that the radially spreadable element is moveable axially within the distance between the first and second limit stops, including the gap distance, without rotation thereof and is contactable with each limit stop; and an interior element having an internal threaded bore and an outer cone tapering towards the free end of the adjusting screw and being structured, dimensioned, and disposed for cooperation with the inner cone of the radially spreadable element, wherein the interior element is screwed onto the adjusting screw and is axially movable with respect to the inner tube by rotation thereof via the internal threaded bore. The radially spreadable element and the interior element cooperate to form a spreading device supported axially at the end of the inner tube, the spreading device for clamping the inner tube within the outer tube, and the adjusting screw is fixed within the outer tube by a plug with a collar facing the spreadable element and the interior element. According to this exemplary embodiment, the interior element comprises a surface facing said collar, which is provided with at least one axial protrusion extending towards said collar. To have such an axial protrusion, i.e. a protrusion protruding from the surface of the interior element facing said collar in axial direction towards an end of the inner tube, prevents that there is a full surface contact between the surface of the interior element facing said collar and the surface of said collar. If such a full surface contact is possible, it may happen that upon complete rotation of the interior element into the position where it is touching the collar it may become friction locked against the collar. This can be prevented by providing such an axial protrusion. 
     In the alternative it is possible that the surface of the collar facing the interior element is provided with at least one axial protrusion extending towards said surface of the interior element, having essentially the same effect, namely that there is no full surface contact in the lowermost position of the interior element but only a small contact area or contact point to avoid friction locking. 
     According to yet another exemplary embodiment, both the interior element as well as the surface of the collar facing the interior element are provided with such protrusions of opposite orientation. 
     Also within this embodiment, the radially spreadable element may have a peripheral slot that extends along an entire axial length of the radially spreadable element. 
     According to yet a further exemplary embodiment, the axial protrusion on the surface of the interior element and/or the axial protrusion on the collar of the plug are wedge shaped. This means that a protrusion on the interior element has a sloped or inclined surface facing (with the inclination angle) the surface of the collar, and it has an axial surface oriented essentially perpendicular to the surface of the collar and to the bottom surface of the interior element. On the other hand this means that the protrusion on the collar has a sloped or inclined surface facing (with the inclination angle) the bottom surface of the interior element and it also has an axial surface oriented perpendicular to the surface of the collar and to the bottom surface of the interior element. The inclination of the sloped surfaces, in both cases, i.e. on the collar as well as on the interior element, preferably has the same inclination as the inclination of the threading of the adjustment screw. 
     According to an even further exemplary embodiment, both the surface of the interior element and the collar of the plug are provided with at least one wedge shaped axial protrusion each, wherein the wedge shaped axial protrusion on the surface of the interior element has a first sloped surface and a first axial surface and the wedge shaped axial protrusion on the surface of the collar of the plug has a second sloped surface and a second axial surface, and wherein the first axial surface and the second axial surface face each other and are contactable (by abutment) by rotation of the interior element via the internal threaded bore. It is, for example, possible to have one such wedge shaped protrusion on the interior element and to have such wedge shaped protrusions on the collar, the latter to being arranged opposite each other. 
     It is generally possible that these protrusions or wedges are one-piece with the interior element and the plug forming the collar, respectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details of the present invention can be derived from the following description, in which the present invention is described in greater detail and is explained on the basis of the exemplary embodiments depicted in the drawing. In the latter: 
         FIG. 1  in a partial longitudinal cutaway and truncated view depicts an adjustable-length pole according to a first exemplary embodiment of the present invention, 
         FIG. 2  depicts a partial longitudinal cutaway view, rotated 90° with respect to  FIG. 1 , of the first exemplary embodiment, 
         FIG. 3  depicts a view along the line III-III of  FIG. 2 , 
         FIG. 4  depicts a representation corresponding to  FIG. 1 , but in accordance with a second exemplary embodiment of the present invention, and 
         FIG. 5  depicts a representation corresponding to  FIG. 2 , but in accordance with the second exemplary embodiment of the present invention and 
         FIGS. 6   a )- f ) depict a third exemplary embodiment with the outer tube removed for better visibility, wherein in  FIGS. 6   a )- 6   d ) provide views from the four different lateral directions are illustrated, in  FIG. 6   e ) a top view is illustrated and in  FIG. 6   f ) a perspective view is illustrated of the spreading device with all parts mounted thereon; 
         FIGS. 7   a )- m ) depict the spreadable element according to the third exemplary embodiment, wherein in  FIGS. 7   a )- 7   d ) views from the four different lateral directions are illustrated, in  FIGS. 7   e ) and  7   f ) a top and bottom view are illustrated, respectively, in  FIGS. 7   g ) and  7   h ) to different perspective illustrations are given, in  FIGS. 7   i ) and  7   k ) the cuts along A-A and B-B as given in  FIG. 7   e ) are illustrated, and in  FIGS. 7   l ) and  7   m ) the cuts along A-A and B-B as defined in  FIG. 7   n ), a top view, are given for the assembled third exemplary embodiment; 
         FIGS. 8   a )- f ) depict the third exemplary embodiment with the spreadable element removed, wherein in  FIGS. 8   a )- 8   d ) views from the four different lateral directions are illustrated, in  FIG. 8   e ) a top view is illustrated and in  FIG. 8   f ) a perspective view is illustrated; 
         FIGS. 9   a )- d ) depict the third exemplary embodiment with the spreadable element and the interior element removed, wherein in  FIGS. 9   a ) and  b ) lateral views rotating by 90° are indicated,  FIG. 9   c ) is a detailed view on the bottom part of the adjusting screw in a magnified representation,  FIG. 9   d ) is a top view and  FIG. 9   e ) is a perspective view; 
         FIGS. 10   b )- g ) depict the interior element of the third exemplary embodiment in the four lateral side views in  FIGS. 10   b )- 10   e ), in an axial cut along the line A-B in  FIG. 10   a ), in a perspective view in  FIG. 10   f ) and in a bottom view in  FIG. 10   g ); and 
         FIG. 11  shows the situation of contact of the axial surfaces of the wedge shaped protrusions in a perspective view. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the connecting segments of an adjustable-length pole  10 ,  110 , depicted in the drawing in accordance with two exemplary embodiments, an inner tube  11  is guided telescope-like in an outer tube  12 . For this purpose, inner tube  11 , at its end  13  that is facing outer tube  12 , is provided with a spreading device  15 ,  115 , using which inner tube  11  can be fixed at any position within the outer tube  12  in a clamping manner. 
     Spreading device  15 ,  115  has an exterior element in the form of a spreading element  16 ,  116 , an interior element  17 , and an adjusting screw, or externally threaded rod  18 ,  118 . Externally threaded rod  18 ,  118 , which is arranged in the axial direction of pole  10 ,  110 , is supported at its one end area in a rotationally fixed manner on insertion end  13  of inner tube  11 . For this purpose, externally threaded rod  18 ,  118  is inserted, or screwed, into an end plug  19 , or is integrally configured on the latter, or the like, and is axially fixed and held in a rotationally fixed manner in the end plug using adhesive or the like. End plug  19  is also axially fixed and supported in a rotationally fixed manner in inner tube  11 . 
     Interior element  17  by its axial central interior thread  21  is screwed onto externally threaded rod  18 ,  118 . Interior element  17  is provided on its exterior side with a cone  22 , or it is configured in a conical manner. Outer cone  22  tapers toward the free end of externally threaded rod  18 ,  118 . Externally threaded rod  18 ,  118  penetrates internally threaded bore  21  of interior element  17  and is connected at its protruding free end in a rotationally fixed manner to an exterior limit stop  26 ,  126 . 
     Exterior-side spreading element  16 ,  116  on its spreadable main body  23 ,  123  has an inner cone, or interior taper  27 ,  127  whose slope corresponds to that of outer cone, or exterior taper  22  of interior element  17 . According to the graphic depiction, interior element  17  is accommodated without play in spreading element  16 ,  116 , which is oriented in the contrary direction, outer cone  22  being shorter than inner cone  27 ,  127 . In accordance with the depicted arrangement, inner cone, or interior taper  27 ,  127  of spreading element  16 ,  116  opens towards the end of inner tube  11 ,  111  from an apex  27 A. By way of example, spreading element  16 ,  116  can be made of plastic, and interior element  17 ,  117  can be made of metal or plastic. 
     Integral end plug  19  is provided with an interior part  31 , which is supported in inner tube  11  so as to be prevented from rotating or sliding, and a collar  32 , which lies on the annular end face of inner tube  11 . Protruding from collar  32  is a guide piece  33  for spreading element  16 ,  116 , the guide piece having a smaller diameter than the latter. 
     Spreading element  16 ,  116  is roughly pot shaped, pot base  36 ,  136  having a through bore  37 ,  137 , which is penetrated by the free end area of adjusting screw  18 ,  118 . Pot base  36 ,  136  is axially movable relative to adjusting screw  18 ,  118 . Main body  23 ,  123  of spreading element  16 ,  116 , which on the exterior periphery can be provided with one or more friction linings, can be coated therewith, or can be configured through its surface composition (for example, longitudinal ribs) so as to achieve an increased frictional force with respect to the interior periphery of outer tube  12 , has, on its end facing away from pot base  36  and facing inner tube  11 , a cylindrical shoulder  38 ,  138 , that is smaller in its exterior diameter, in which guide piece  33  can engage at its end side. In this context, between guide piece  33  and spreading element  16 ,  116 , enough play is available, so that the latter can move unhindered both axially and radially. Therefore, spreading element  16 ,  116  is axially movable within narrow limits between a first, outer limit stop  26 ,  126  on the free end of adjusting screw  18 ,  118  and a second, inner limit stop  28 , which is formed by the annular surface of collar  32  around guide piece  33 . The distance between the surfaces of the first limit stop  24 ,  124  and the second limit stop  28  is somewhat greater than the axial length of spreading element  16 ,  116  between the exterior surface of pot base  36  and the annular end face of cylindrical shoulder  38 ,  138 . 
     In the exemplary embodiment of  FIGS. 1 through 3 , first or outer limit stop  26  is formed by a cap  26 ′, which is attached to the free end of adjusting screw  18 , for example, by being screwed, pressed, glued, plastic-extruded, or attached in some other way. Cap  26 ′ has a radial edge  24  acting as a limit stop surface  24 , which can come into contact with spreading element  16 . 
     In the exemplary embodiment of  FIGS. 4 and 5 , outer limit stop  126  is configured as a head  126 ′ that is formed on the free end of adjusting screw  118 , interior annular surface  124  of the head constituting the limit stop surface for spreading element  116 . 
     Interior element  17  on each of two diametrically opposite peripheral areas of outer cone  22  has a plurality of fins  41 , whose longitudinal end face runs parallel to the stick axis. Each fin  41  is axially guided in a correspondingly wide slot  43 ,  44 , and  143 ,  144  of spreading element  16 ,  116 . In this manner, when interior element  17  moves axially relative to spreading element  16 ,  116 , it cannot rotate with respect to the latter. Both slots  43 ,  44 , and  143 ,  144  are provided essentially over the longitudinal extension of main body  23 ,  123  of spreading element  16 ,  116 , i.e., they only penetrate into the area of cylindrical shoulder  38 ,  138  to an insignificant extent. In other words, this also means that the greatest radial dimension of diametrically opposite fins  41 , is equal to the interior diameter of cylindrical shoulder  38 ,  138 . 
     As can be seen from  FIG. 3 , which essentially applies to both the first and second exemplary embodiments, spreading element  16 ,  116  is furnished on its exterior periphery with four notches  46 ,  146  that are all axially and centrally symmetrical to each other, which run in the longitudinal direction and extend over virtually the entire length of main body  23 ,  123  of spreading element  16 ,  116 . 
     Generated in this manner are defined, peripheral clamping areas of spreading element  16 ,  116 . In the first exemplary embodiment of  FIGS. 1 through 3 , after spreading device  16  is fixed in inner tube  11 , interior element  17  is screwed onto the free end of adjusting screw  18 , and thereafter spreading element  16  is placed over adjusting screw  18 . Subsequently, exterior limit stop  26  is attached at the protruding end of adjusting screw  18 , after which the end of inner tube  11 , which has been completed in this manner, can be inserted into outer tube  12 . 
     In the second exemplary embodiment of  FIGS. 4 and 5 , in which adjusting screw  118  has molded head  126 ′ and in which interior element  17  is screwed from the other side of adjusting screw  118 , before adjusting screw  118  has been fixedly joined to end plug  19 , spreading element  116  (if it has not been threaded first) must subsequently be placed over adjusting screw  118  and interior element  17 . For this purpose, spreading element  116  according to  FIG. 5  has an axially continuous slot  148 , at which spreading element  116  can be opened radially and placed over interior element  17  and adjusting screw  118 . In the depicted second exemplary embodiment, continuous slot  148  is partially identical with one of slots  143 ,  144 , although it is narrower in the area that extends further. 
     In response to the motion of clamping inner tube  11  in outer tube  12  using spreading device  15 ,  115 , interior element  17  is moved away from inner tube  11  in the direction of arrow A by rotating inner tube  11  and therefore adjusting screw  18 ,  118  to the right (in the case of a left-handed thread) or to the left (in the case of a right-handed thread) with respect to outer tube  12 , spreading element  16 ,  116  first being moved, or pushed, in the same direction up to exterior limit stop  26 , 126 . Thereafter, in response to a further axial motion of interior element  17 , spreading element  16 ,  116  is spread apart radially in the direction of arrow A, so that the exterior circumference of spreading element  16 ,  116  under pressure contacts the interior circumference of outer tube  12 . In this state, the annular end face of cylindrical shoulder  38 ,  138  of spreading element  16 ,  116  has a specific, preestablished, slight distance a from inner limit stop surface  28  of collar  32 . Then, inner tube  11  being clamped in outer tube  12  using a more or less high torque, if an impact-like axial stress is exerted from outer tube  12 , which is provided, for example, with a handle, onto inner tube  11 , which is provided with a stick tip, then due to the clamping fixation of spreading element  16 ,  116  in outer tube  12 , interior element  17  can move axially. This means that interior element  17  moves further into interior cone  27 ,  127  of spreading element  16 ,  116 , which leads to a further spreading of spreading element  16 ,  116  and therefore to an increase in the holding force between interior tube  11  and outer tube  12 . 
       FIGS. 6-11  show a third exemplary embodiment of the present invention, wherein in  FIG. 6  this spreading device  15  is shown in an assembled state but with the outer tube removed for better visibility, in  FIG. 7  the spreading element  16  is shown in different views and also some axial cuts of the assembled device, in  FIG. 8  the spreading device  15  is shown with the spreading element  16  removed to show the interior element  17  as mounted on the adjusting screw  18  in more detail,  FIG. 9  shows the spreading device  15  with spreading element  16  and interior element  17  removed,  FIG. 10  shows the interior element  17  in different views and  FIG. 11  shows in a perspective view how the protrusions  25  on the interior element and  28  on the collar  32  of the plug  19  contact each other. 
     As one can see from  FIG. 6  and  FIG. 7 , the spreading element  16  in an axial direction again comprises, at its end facing the interior tube  11 , a cylindrical shoulder  38 , wherein the outer diameter is significantly smaller than the inner diameter of the outer tube, so cylindrical shoulder  38  is not contacting the inner surface of the outer tube  12  if clamping it. Above cylindrical shoulder  38  there is the spreadable main body  23  of the spreading element. This main body  23  is provided with axial recesses  39  which give rise to protrusions  40 . As a result, the outer cylindrical surface of this spreadable main body  23  does not contact the interior surface of the outer tube in a full surface contact but only in those surface areas which are not recessed by the four axial recesses  39 , as seen also in  FIG. 7 . 
     As in the case of the second exemplary embodiment, the spreadable element  16  comprises two slots  143  and  144  for engagement of the fins  41 ,  42 , respectively, of the interior element  17 . One of these slots  144  is axially discontinuous, i.e. at the position of this slot  144  the main part of the cylindrical shoulder  38  is not interrupted by the slot. The slot  144  has a bottom  45  which is sufficiently low such that if, as illustrated in  FIG. 6   b ), the interior element  17  is in its lowermost position and in contact with the plug  19  or the wedge  28 , the bottom end of the corresponding fin  42  of the interior element  17  may just about or not even contact this bottom  45  in a position where still the spreading element  16  contacts the upper limit stop  26  and where there is a gap distance illustrated with y. The parameter y is normally in the range of 0.1-1.5 mm. 
     Opposite said discontinuous slot  144  there is provided in the spreadable element  16  an axially continuous slot  148 , which extends through the full axial length of the spreadable element  16 . 
     The pot base of the spreadable element  16  is provided with a through bore with an inner diameter larger than the outer diameter of the screw  18  and not provided with a threading, so the spreadable element  16  can move along the screw  18  without rotation of the spreadable element  16 . 
     To have one discontinuous slot  144  at one side and one continuous slot  148  at the opposite side in the spreadable element  16  has the advantage that, for assembly of such a spreading device  15 , the spreading element  16 , which usually is made of a polymer material, can be forced apart along the axially continuous slot  148  such that the two halves joined by the cylindrical shoulder part  38  below the above-mentioned bottom  45 , can be opened and the whole spreading element  16  can be shifted from a lateral direction onto the spreading device, more specifically onto the interior element  17  mounted on the screw  18 , as illustrated in  FIG. 8 . 
     As can be seen in particular from  FIGS. 8 and 10 , the interior element  17  in this case is provided with fins  41 ,  42  extending much further in a radial direction than in the previous exemplary embodiments. In this case also, at their bottom end, the fins extend by a radial width  14  in a radial direction beyond the surface of the cylindrical part of the interior element. The radial width  14  is typically in the range of 0.5-2.0 mm. 
     The interior element  17  correspondingly comprises a cylindrical part  20 , which is essentially located in a cylindrical recess in the region of the cylindrical shoulder  38  of the spreading element  16 , and a conically converging part which forms the cone  22  of the interior element  17 . Typically the inclination angle of this cone  22  with respect to the axial direction is small, i.e. below 10° typically it is in the range between 3-5°. The inclination angle of the corresponding interior surface  27  of the spreadable element  16  is essentially complementary thereto. The fins  41 ,  42  are only provided in the region of the cone  22 . They extend over the full length of the cone  22 . The fins  41 ,  42 , of which two are located opposite each other, typically have a thickness  14   a  in the range of 0.5-1.5 mm. 
     At the bottom end of the interior element  17  there is an essentially flat bottom surface  24  facing the collar  32  of the plug  19 . According to this embodiment, on this surface  24  there is provided a wedge shaped protrusion  25 , which extends in an axial direction towards the collar  32 . It has an inclined or sloped surface facing the plug, which smoothly passes into the bottom surface  24 , and it has an axial abutment surface  34 . The two surfaces converge at a ridge of the ramp  25 . Typically the wedge shaped element  25  extends over 90 degrees of the circumference of this bottom surface  24 . The inclination of the sloped surface of the ramp  25  is essentially along the same direction as the threading of the adjusting screw  18 . It may, however, have a different size of the pitch. 
     As can be seen from  FIGS. 7   l ) and  7   m ), the surfaces  22  and  27  are essentially parallel, and if the interior element  17  is in the bottommost position, the fin  42  located in slot  144  does not even reach bottom  45 , even if the spreadable element  16  is in contact with exterior limit stop  26 . As the inner tube and, correspondingly, the plug  19  is rotated, interior element  17  travels upwards without rotation thereof (also the spreadable element  16  is not rotating, the two being interlocked by fins and slots, as concerns rotation) until surface  22  contacts surface  27 . If then rotation continues, interior element  17  is forced into spreadable element  16  pushing the spreadable main body  23  apart in axial direction, thus clamping the outer tube. 
     On the upper surface  30  of the collar  32  of the end plug  19 , at the same radial distance from the center axis of the adjusting screw there is provided two protrusions  28  on the collar  32 . These protrusions  28  are also wedge shaped ramps  28  with an inclined surface with the same direction of inclination as the inclined surface of the ramp  25  (however with a different size of each possibly), and with, as best visible in  FIG. 9 , an axial abutment surface  35 . This abutment surface  35  is facing the abutment surface  34  on the interior element  17  such that, as illustrated in  FIG. 11 , if the interior element  17  is rotated on the adjusting screw  18  by rotation of the interior element with respect to the adjusting screw to its bottommost position, the two surfaces  34  and  35  will abut on each other and correspondingly full surface contact of surfaces  24  and  30  is avoided and correspondingly also frictional locking between the interior element  17  and collar  32  is not possible. 
     LIST OF REFERENCE NUMERALS 
     
         
           10 ,  110  adjustable-length pole 
           11 ,  111  inner tube 
           12 ,  112  outer tube 
           13 ,  113  end of inner tube facing outer tube 
           14  radial width of fin at lower end 
           14   a  thickness of fin 
           15 ,  115  spreading device 
           16 ,  116  spreading element 
           17 ,  117  interior element 
           18 ,  118  externally threaded rod, adjusting screw 
           19 ,  119  end plug 
           20  cylindrical part of interior element 
           21 ,  121  axial central interior thread of interior element 
           22 ,  122  cone of interior element 
           23 ,  123  spreadable main body of spreading element 
           24  bottom surface of interior element 
           25  ramp on bottom surface of interior element, wedge 
           26 ,  126  exterior limit stop 
           27 ,  127  inner cone, interior taper 
           28  ramp on collar of end plug 
           29  tapered portion of adjusting screw 
           30  upper surface of collar 
           31 ,  131  interior part of end plug 
           32 ,  132  collar of end plug 
           33 ,  133  guide piece of end plug 
           34  axial abutment surface of ramp on interior element 
           35  axial abutment surface of ramp on collar 
           36 ,  136  pot base of spreading element 
           37 ,  137  through bore through pot base 
           38 ,  138  cylindrical shoulder of spreading element 
           39  axial recess in spreading element 
           40  axial protrusion of spreading element 
           41 ,  141  fin 
           42 ,  142  fin 
           43 ,  143  slot 
           44 ,  144  slot 
           45  bottom of axially discontinuous slot 
           148  axially continuous slot 
         y gap distance for the situation when the spreadable element is in contact with upper limit stop