Abstract:
A walking aid comprises a shaft and a foot assembly, in which the foot assembly includes in combination a sleeve member and a foot member adapted for relative axial sliding movement and including resilient movement-restraint means, the sleeve member being adapted for attachment to the shaft and including grip means for inhibiting or preventing removal from the shaft once attached thereto.  
     The resilience may be adjustable and the foot member is preferably free to swivel within the sleeve member. The assembly may also be used as a castor, for use for example in shopping trolleys.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to walking aids with resiliently-mounted feet, intended to alleviate problems experienced by users of conventional walking aids arising from shock loading transferred to the muscles of the hands, wrists, arms and shoulders; and to other apparatus incorporating resiliently-mounted feet or castors.  
         BACKGROUND OF THE INVENTION  
         [0002]    Physiotherapists have evidence that suggests that the muscles of the shoulder in particular and the muscles of the hands, wrists and arms are stressed when using normal walking aids. Persons who have sustained several tears of the muscles of the shoulder tend to experience difficulty when using a rigid, uncushioned walking stick, crutch or Zimmer frame. Similarly, persons who have osteo-arthritis or rheumatoid arthritis often experience problems when using rigid support aids. Those who have hip and knee arthritis and have rotator cuff regeneration or tears in the shoulder also tend to be uncomfortable with rigid walking aids.  
           [0003]    In order to alleviate such problems, walking aids with shock-absorbing feet have been proposed. One such device is described in GB-A-23 18510, in which the foot member slides telescopically over an upper sleeve, a spring providing for resilience in the sliding movement. However, in order to provide selective resilience according to the weight of the user, it is necessary to change the spring for another one of different spring rate. Additionally, although prior art shock-absorbing feet can be retrofitted to existing walking aids, there is a tendency for the feet to work loose and even to become detached from the shaft of the walking aid in use.  
           [0004]    What has been needed but heretofore unavailable is a walking aid with a resiliently mounted foot that does not suffer from the above disadvantages of the prior art.  
           [0005]    It is desirable that the ground-contacting ferrule of a walking aid can rotate axially with respect to the shaft, in order to promote user comfort and convenience. However, it has been found in practice that freedom of rotation in known apparatus, while not necessarily theoretically excluded, is in practice not smooth but on the contrary is subject, under twisting movement exerted by the user on the handle, to intermittent periods of rotational freedom separated by intervals of sticking, in which static friction and kinetic friction alternate with consequential rotational jarring experienced by the user.  
           [0006]    In an attempt to overcome this problem, it has been proposed to introduce ball or roller bearings to enhance the freedom of rotation but it has surprisingly been found that the resulting walking aid is potentially disadvantageous or even dangerous in that, if placed on the ground at an angle to the vertical, the ferrule tends to rotate under pressure, resulting in the lower end of the shaft moving sideways and the walking aid failing to support the user&#39;s weight. There has thus long existed a need for an improved walking aid that includes, for example, a rotatable ground-contacting ferrule that provides for controlled or limited but nevertheless smoothly operating rotation.  
         SUMMARY OF THE INVENTION  
         [0007]    According to one aspect of the present invention, a walking aid comprises a shaft and a foot assembly, in which the foot assembly comprises in combination a sleeve member and a foot member adapted for relative axial sliding movement and including spring means resiliently to restrain said sliding movement, the sleeve member being adapted for attachment to the shaft and including grip means for inhibiting or preventing removal from the shaft once attached thereto.  
           [0008]    The shaft may be the leg or a leg of a crutch or walking frame or may be attached to the lower end of such a leg, which includes solid and tubular legs.  
           [0009]    In another aspect, the invention provides a foot assembly suitable for attachment to the shaft of a tubular walking aid or a tubular leg of a walking aid, the foot assembly comprising in combination a sleeve member and a foot member adapted for relative axial sliding movement and including spring means resiliently to restrain said sliding movement, the sleeve member including grip means for inhibiting or preventing removal from the tubular leg once attached thereto.  
           [0010]    Preferably, the foot member comprises a base element to which a conventional rubber or plastics ferrule or shoe is attached, the base element being connected to a neck member which is journalled in the sleeve member with a compression spring therebetween, the neck member being provided at its upper or distal end with a screw thread to receive a retaining and resilience-adjustment nut. One or more bushes, also known as bushings, may be provided between the neck and sleeve members to facilitate axial sliding movement and, desirably, a relative axial rotational ability.  
           [0011]    The grip means may comprise a resiliently-compressible element associated with the sleeve member for force-fitting within the shaft, whereby the sleeve member is retained within the shaft by friction forces acting between the resiliently-compressible member and the internal wall of the shaft. Preferably, however, the grip means comprises an element adapted to permit the sleeve member to be slidingly inserted within the shaft but which expands radically to assume a jamming position on attempted withdrawal thereof. Such an arrangement may be provided by for example an expandable ring such as a rubber or plastics O ring or a snap-ring, which may also be made from metal, carried in an annular groove formed in the external surface of the sleeve member, the groove having a sloping or chamfered wall which urges the ring to expand to jam against the shaft wall on relative movement between the sleeve member and shaft in a direction of movement whereby the sloping or chamfered wall is the trailing or rear wall.  
           [0012]    When using walking aids according to the invention, the user experiences more surefooted ground contact than with rigid devices, even on slippery surfaces, the light spring force ensuring a more stable initial contact and the full load being gradually applied as the spring compresses. There is thus less of a tendency for the foot to slip or skid away when placed on the ground at an angle to the vertical. Furthermore, the sleeve member is desirably free to rotate axially about the foot member; such freedom of rotation not only promotes even wear and hence a considerably extended life to the ground-contacting ferrule but also manifestly improves user comfort and convenience, in that any twisting motion as between the user and the walking aid is more readily accommodated by the walking aid.  
           [0013]    In yet another aspect, the present invention provides walking aid apparatus comprising a handle portion and a shaft portion including a ground-contacting ferrule, the apparatus comprising telescopically-mounted relatively rotatable elements and spring means acting between said elements resiliently to restrain relative compression movement, in which the bearing surfaces of the spring means and at least one element comprise sliding friction-reducing materials whereby rotation between the handle portion and the ferrule accommodates twisting movement as between the user and the ground in a controlled manner.  
           [0014]    By “sliding friction-reducing materials” in this specification is meant a materials couple which reduces the friction between at least one end of the spring means and the associated element, relative axial rotation being accommodated by sliding movement therebetween. It has been found that the use of sliding friction-reducing materials results in controlled rotation as between the spring means and at least one of the telescopic elements with considerable benefits to the user in avoiding tortional loading to the wrist, elbow and/or shoulder joints which can be especially painful to those who suffer from arthritis, without the disadvantages arising from uncontrolled rotation such as results from the use of ball or roller bearings.  
           [0015]    The bearing surface of the at least one element which is capable of axial rotation relative to the spring means may be an integral part of the element itself or alternatively may comprise a separate friction-reducing element having a spring-contacting surface and an oppositely-facing surface which bears against a seat of said element, rotational sliding movement taking place between the spring means and the separate element and/or between the separate element and the seat. The sliding friction-reducing element preferably comprises an annular washer, which may be configured as a cup washer, the cup comprising the spring-facing surface and a peripheral wall to encompass the extremity of the spring means. The material from which the sliding friction-reducing element is formed should preferably be sufficiently hard to be accurately machined with a substantially flat seat-facing area while providing for the required degree of friction with the other material of the couple to give controlled rotation under load conditions. Suitable materials include engineering plastics materials such as acetal-type copolymers which may optionally be glass- or fiber- reinforced. However, the choice of material is to some extent governed by the diameter of the ferrule or at least the ground-contacting lower surface thereof, since a larger-diameter ferrule will have a greater resistance to twisting movement on the ground and, hence, a material with less inherent lubricity is preferred for the friction-reducing means, in order to provide the desired controlled rotation. Where the seat of the telescopic element bears directly on the spring means, similar criteria as to the choice of materials apply.  
           [0016]    The telescopically-mounted relatively rotatable elements typically comprise an outer sleeve element and an inner spindle element, the elements being capable both of relative axial sliding movement to accommodate compression and expansion as a load is applied to or released from the handle portion of the apparatus and of relative axial rotation to accommodate twisting movement as between the user and the ground in use.  
           [0017]    The spring means may be any resilient element and may comprise for example a helical spring, a pneumatically- or hydraulically-controlled strut or a resilient elastomeric material; conventionally, a helical stainless steel spring is used but other resilient materials or assemblies may equally be used in the inventive apparatus. The inner or spindle telescopically-mounted element may have an inner co-axial neck portion of reduced diameter, an annular gap being defined between the neck portion and the sleeve element and which accommodates the spring means which, conveniently, comprise a helical spring. However, in another arrangement, the inner telescopically mounted element has an inner end face which bears, directly or via a friction-reducing element, on one end of the spring means. In such an arrangement, the spring means may comprise a block, typically a cylindrical block, of resilient elastomeric material. In yet another arrangement, the spring means bears directly on the ferrule or is integrally formed with the ferrule from a suitable elastomeric material. The spring means is preferably pre-loaded so that, even when in the fully-extended position of the telescopically-mounted elements, the spring means nevertheless remains partially compressed, thereby causing the apparatus to exhibit the controlled rotation property under a no-load or very light loading exerted on the apparatus through the handle portion.  
           [0018]    Preferably, the apparatus includes cylindrical bushes journalled between the cooperating axially slidable surfaces of the telescopically mounted elements, the bushes enhancing the relative axial sliding movement and optionally assisting to a lesser extent in the controlled rotation. The bushes are preferably formed from a suitable plastics material which may comprise nylon or an engineering plastics as in the case of the sliding friction-reducing element.  
           [0019]    The use of a pneumatically- or hydraulically-controlled strut, for example a nitrogen-damped cylinder and piston, for the spring means is advantageous in that the damping force may be adjusted according to the weight of the user by pre-loading to a particular desired gas pressure, for example by the physiotherapist. The ability to increase or decrease the pressure enables stocks of a single unit to be maintained, to be selectively adapted to the requirements of the individual user at the time of supply.  
           [0020]    In an alternative way of pre-loading the spring means, the distal end of the inner telescopically-mounted element may comprise a screw-threaded portion carrying a lock nut which bears on the outer element to adjust its position relative to the inner element, thereby compressing the spring means. The distal end of the outer element may have a counter-bore to accommodate the lock nut; the open end or mouth of the counter-bore may accommodate resilient damping means to act as a cushion for the distal end of the inner element and lock nut on full-load compression of the spring means. Additionally, the proximal end of the outer element, which in use accommodates the spring means, may be formed with an annular groove formed in the wall thereof and which carries a resilient O-ring, preferably supported on an inner-extending shoulder constituted by one wall of the groove. Where the inner element comprises a smaller-diameter neck portion extending co-axially of the cylindrical portion for carrying the spring means and the pre-loading lock nut, an annular shoulder is defined between the cylindrical portion and the neck portion and which makes contact with the O-ring at the position of maximum compression movement while still retaining the ability for controlled rotation. Desirably, where cylindrical bushes are contained in such an arrangement, they are journalled at the proximal end between the cylindrical portion and the inner-facing wall of the sleeve element and at the distal end between the plain part of the neck portion and a smaller-diameter portion of the sleeve element.  
           [0021]    The sub-assembly comprising the telescopically-mounted elements and spring means may be carried, in walking aid apparatus according to the invention, either towards the ferrule end or towards the handle portion end, or indeed at any intermediate location. It has been found in practice, particularly for use by people who are relatively infirm, that provision of the sub-assembly close to the handle portion gives a greater sense of control and hence a greater sense of security.  
           [0022]    The shaft portion of walking aid apparatus according to the invention may comprise an aluminum tube, as in many walking sticks or Zimmer-frames used by people under medical supervision, but may equally be a conventional solid, for example wooden, shaft, if appropriate including a tubular portion for receiving a foot assembly as hereinbefore described, since the invention provides benefits to walking aids such as conventional walking sticks where there is no particular medical condition which requires the use thereof. When used with a metal tubular walking aid, the inner element may be mounted in the tube, whether at the top or bottom thereof, by means of an arrangement as described and comprising grip means for inhibiting or preventing removal from the shaft once attached thereto. Particularly when attached to the upper end of the shaft, both the inner and outer elements may be carried respectively in a cylindrical tube attached to the handle and to the cylindrical shaft using such a grip means. Plastics materials may also be used for the shaft and/or for one or all of the components of the telescopically mounted sub-assembly, provided that the required degree of controlled rotational ability is exhibited as a function of the frictional forces between the rotational bearing surfaces.  
           [0023]    In order to avoid any possibility of a pinching movement as between the outer telescopically-mounted element and the shaft or handle portions in a position at or approaching maximum compression thereof, at least one of the facing edges of the outer element and the shaft or handle portions, preferably both, may be provided with a chamfer so that, even when fully compressed, there remains an annular V-shaped gap between the outer walls thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which:  
         [0025]    [0025]FIGS. 1 and 2 show respectively a sleeve member and foot member of one embodiment of a walking aid,  
         [0026]    [0026]FIG. 3 shows in partial elevation and partial longitudinal section a sleeve member and foot member incorporating variants of the embodiment of FIGS. 1 and 2, assembled together with a compression spring;  
         [0027]    [0027]FIGS. 4 and 5 show the embodiment of FIG. 3 inserted in a shaft respectively in the fully expanded and fully compressed conditions;  
         [0028]    [0028]FIG. 6 shows the general assembly of apparatus according to another embodiment of the invention for fitting to the upper or lower section of a walking aid and containing a helical spring;  
         [0029]    [0029]FIG. 7 shows the assembly of FIG. 6 attached to the lower end of a walking aid the shaft of which has a hollow metal tube;  
         [0030]    [0030]FIG. 8 shows the assembly attached to the lower end of a conventional wooden walking stick;  
         [0031]    [0031]FIG. 9 shows the assembly as attached to the upper end of a walking aid having a hollow metal shaft;  
         [0032]    [0032]FIG. 10 shows an embodiment with a compressible rubber spring; and  
         [0033]    [0033]FIG. 11 shows another embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]    Referring first to FIGS. 1 and 2, the sleeve member  10  is cylindrical in cross section and has an enlarged-diameter lower end flange  11  defining an annular shoulder  12 . The sleeve member has a through-bore  13  which has an enlarged-diameter part  14  at the lower end. The external wall carries a pair of annular grooves  15 ,  16 . The foot member  20  is a cylindrical bar having a lower end  21  of maximum diameter and formed with an axial cavity  22 , a first intermediate zone  23  of reduced diameter, a second intermediate zone  24  of further reduced diameter and defining a shoulder  25  and a screw-threaded upper end  26 . The diameter of first intermediate zone  23  is such that it will slide within the enlarged-diameter bore  14  of the sleeve member and the diameter of second intermediate zone  24  is such that it will slide within the reduced-diameter bore  13  of the sleeve member. A compression spring can be accommodated in the annular gap between the second intermediate zone  24  of the foot member and the enlarged-diameter bore  14  of the sleeve member, as illustrated in and described with reference to FIG. 3. The spring may have a free length of between 25 and 40 mm, for example  32  mm, with up to ten active coils, for example seven coils, and may be made from music wire or stainless steel of diameter 0.75 to 2.0 mm, for example 1.6 or 1.8 mm. The grooves  15 ,  16  are for accommodating expandable O rings or snap rings.  
         [0035]    With reference to FIG. 3, the foot member  20  is shown slidingly inserted in sleeve member  10  with a compression spring  31  carried in annular gap  32  between the members. A washer  33  and nut  34 , preferably of the self-locking type, are inserted over and on the screw-threaded end  26  of the foot member. A diametral hole  35  formed through the walls of the cavity  22  can accommodate a screwdriver or other suitable tool to restrain the foot member from turning as the locknut is tightened. A conventional rubber shoe  36  is applied over the lower end  21  of the foot member. O rings or snap rings  37 ,  38  are contained in the annular grooves.  
         [0036]    The variants of FIG. 3 are firstly bushes  39 ,  40  which are carried in corresponding additional bore zones of the sleeve member and are intended to assist sliding movement of the foot member within the sleeve member; the bushes may be formed from nylon, polytetrafluoroethylene (“PTFE”), or other suitable material. Secondly, the lower annular groove  16  of the sleeve member is formed with a 20° chamfer  41  to the upper wall, whereby the O ring or slip ring  38  contained in the groove is constrained by friction against the inner wall of the shaft, on any attempt being made to withdraw the assembly from within the shaft, to travel up the chamfered surface to expand the ring into jamming relationship with the shaft, thereby preventing or at least inhibiting removal of the assembly from the shaft.  
         [0037]    With reference to FIGS. 4 and 5, the assembly of FIG. 3 is shown inserted in the lower end  42  of a tubular walking stick or crutch shaft, with the bottom of the shaft abutting against the shoulder  12  of the sleeve member. FIG. 4 illustrates the extended condition with no loading on the foot member, whereby the compression spring  31  urges the foot member to the maximum extent below the sleeve member, as determined by the washer  33  and nut  34  engaging the upper end of the sleeve member. FIG. 5 illustrates the maximum compressed condition under axial loading on the foot member, whereby adjacent coils of the spring  31  are urged into contiguous relationship.  
         [0038]    It will be appreciated that the nut can be adjusted to pre-load the spring to adjust the resilience thereof; such adjustment may be carried out either with the foot assembly in place within the shaft, by using a suitable socket spanner and extension bar, or after manually removing the foot assembly by twisting and pulling against the jamming effect. If necessary, the spring can be exchanged for another spring of different rate; again, this can be done in situ by removing the nut, whereupon the foot member and spring can be withdrawn from within the sleeve member.  
         [0039]    Where the locking ring is an O ring, the desired spring strength for the user may conveniently be pre-set by initially rolling the lower O ring  38  out of groove  16  and down the sleeve member until it abuts shoulder  12 . The assembly may then be inserted in the shaft to test whether the spring strength is correct and if necessary withdrawn for adjustment without bringing into effect the jamming action of the assembly within the shaft. When the spring strength is correct, the O ring is then rolled back into groove  16  and the assembly re-inserted in the shaft, where it will be retained by virtue of the jamming effect between the O ring and the interior surface of the shaft. The O ring  37  in the upper groove  15  provides ordinary resilient sealing between the sleeve and foot members and allows insertion and withdrawal with friction but does not provide any jamming or locking effect.  
         [0040]    In an alternative arrangement, the cylindrical bar  20  is inverted and is integral with or attached to the shaft  42 , the sleeve member  10  is carried on the bar with the lock nut  34  facing down and a ferrule  36  is attached to an outer sleeve member engaged in jamming relationship with the O rings of the sleeve member  10 . Access to the locknut is therefore from the lower end of the shaft, for example after removal of the ferrule.  
         [0041]    Referring to FIG. 6, a lower part  61  of the hollow shaft of a walking aid is attached to an upper part  62  of the shaft via a telescopically-mounted spindle element  63  and a sleeve element  64 . The sleeve element is carried in the upper end of the shaft  61  and is held therein by rubber or plastic expandable O-rings  65 ,  66  that are carried in annular grooves, the groove which accommodates O-ring  66  having a lower chamfered wall  67 , whereby the ring  66  is forced into jamming engagement with the inner wall of the shaft  61  on any attempted withdrawal of the sleeve element  64  from the shaft, thereby preventing such withdrawal. The spindle element  63 , about which the sleeve element can rotate, consists of a spindle body  68 , a neck  69  and a base  70 , the base being similarly inserted in the lower end of the shaft  62  and retained therein by O-rings  71 ,  72  carried in annular grooves, the lower groove which accommodates ring  72  having an upper chamfered wall  73 . The upper end of the shaft  61  is formed with a sloping edge  61   a  and, similarly, the lower-facing edge of the base  70  of the spindle element is formed as a sloping shoulder  70   a.    
         [0042]    The spindle element is journalled for axial sliding movement in the sleeve element by means of annular bushes  74 ,  75  and a helical spring  76  extends between an upper shoulder formed between the body  68  and neck  69  of the spindle element and an inner shoulder at the lower end of the sleeve element. An O-ring  77  is carried in an inner-facing intermediate annular groove in the sleeve element and serves as a resilient buffer for contact with the upper shoulder on maximum depression of the spindle element within the sleeve element.  
         [0043]    At each end of the spring  76  and journalled respectively between the machined ends of the coils thereof and the upper and lower shoulders are sliding friction reducing clutch washers  78 ,  79  formed from an acetal copolymer. The spindle element  63  is retained within the sleeve element  64  by a locknut nut  80  applied to the lower screw threaded end of the neck  69  and bearing against the lower annular surface of the sleeve element via a nylon washer  81  and a rubber washer  82 . Once suitable locknut includes, for example, a Nyloc nut, which is available from Automotion International, Ltd., Saddleworth Business Centre, Huddersfield Road, Delph, Oldham, OL3 5DF, Great Britain.  
         [0044]    In the position shown in FIG. 6 with the spindle element at its position of maximum extension within the sleeve element, the spring  76  still exerts pressure as between the respective elements through the clutch washers  78 ,  79 . The clutch washers enable smooth relative axial rotation as between the respective elements and, therefore, between the shaft parts  61 ,  62 , avoiding on the one hand intermittent grip and release which would otherwise occur from direct metal-to-metal contact between the ends of the spring and the respective shoulders while, on the other hand, preventing uncontrolled or excess rotation. A similar effect is achieved when compression pressure is applied by a user so that the spindle element slides within the sleeve element against the pressure exerted by spring  76  until, at the position of maximum compression, the upper shoulder is in contact with O-ring  77 . At this position, the sloping ends  61   a ,  70   a  of the shaft  61  and base  70  of the spindle element  62  are in abutting relationship, the sloping surfaces preventing any possibility of the user&#39;s skin or clothing being pinched between the ends of the shafts.  
         [0045]    With reference to FIG. 7, an arrangement similar to that described with reference to FIG. 6 is shown but the sleeve element  83  constitutes the lower end of the shaft of the walking aid and carries a rubber ferrule  84 . Resilient disks  85  are carried at the lower end of the sleeve element  83 , to act as a bump-stop for the end of the neck portion  69  of the spindle element.  
         [0046]    [0046]FIG. 8 shows an arrangement similar to that described with reference to FIG. 7 but the upper end of the spindle element is formed as a hollow, blind-ended cylinder  86  which receives the lower end of a solid shaft  87  of a walking aid.  
         [0047]    [0047]FIG. 9 illustrates a further embodiment in which the spindle element/sleeve element assembly is carried at the upper end of a walking stick shaft  88 , immediately beneath the handle  89 . The upper end of the spindle element is secured, in a manner similar to that described with reference to FIG. 6, in the lower end of a short piece of tubing  90 , the upper end of which carries a splined element  91  secured within a cavity formed within the handle  89 .  
         [0048]    In the embodiment illustrated, hollow shafts are formed from aluminum and solid shafts are formed from wood; the respective spindle and sleeve elements are formed from aluminum, although the sleeve element may be made from stainless steel. In a further embodiment, the arrangement as described with reference to FIG. 7 could be inverted so that the ferrule is attached to the enlarged body part of the spindle element and the sleeve element is held within the lower part of the shaft of the walking aid with the lock nut facing upwardly in the shaft.  
         [0049]    As shown in the embodiments illustrated in FIG. 6 to  9 , the base of the spindle element is preferably adapted to receive a connector part either for fitting within the shaft of a walking aid or around the lower end thereof, or to which a ferrule may be directly attached. As illustrated, the base of the spindle element is formed with an axial cavity to receive the spigot or stub end of the connector part, although the connector part could equally include a cavity to receive a spigot or stub end of the spindle element.  
         [0050]    With reference to FIG. 10, a sub-assembly suitable for fitting to the upper or lower end of a walking stick shaft consists essentially of a cylindrical sleeve  101 , a piston or plunger body  102  for fitting within the sleeve and a resilient cylindrical rubber block  103  carried within the cavity of the sleeve. Once assembled, the plunger body is held captive within the sleeve by cooperating inner and outer annular shoulders  104 ,  105 ; an O-ring  106  is provided in a groove below shoulder  105  to act as a resilient buffer under maximum extension of the plunger with respect to the sleeve. The lower end of the rubber block  103  bears against the upper end surface  107  of the plunger body and the upper end of the block bears against and is retained by a disc  108  threadably engaged in the upper end of the sleeve  101 .  
         [0051]    A ferrule (not shown) may be attached to the foot  109  of the plunger which, as shown, is threadably attached thereto after insertion from above of the plunger body. The sleeve and plunger may be formed from a plastics material such as polypropylene or polybutylene. The foot of the plunger may of course be attached to the plunger body by means other than screwing, such as by the use of a glue or a solvent for plastics materials, thus welding them together.  
         [0052]    In use, the plunger body is axially rotatable within the sleeve but is restrained from uncontrolled rotation by frictional forces between the mating surfaces of the rubber block  103  and the plunger body.  
         [0053]    Referring to FIG. 11, another embodiment of a sub-assembly fitted to the lower end of a tubular shaft  110  consists of an adapter  111  fitted within the lower end of the shaft end a piston or plunger  112  secured within and extending axially from the adapter. The plunger  112  slides within a cylindrical sleeve  113  and is held captive therein by cooperating inner and outer annular  114 ,  115  via O-ring  116 . A clutch washer  117  is provided at the lower end of the plunger for mounting one end of a spring  118 , the other end being retained by plug  119  retained at the bottom of the sleeve  113 . A ferrule  120  is carried at the lower end of the sleeve  113 . The spring may be a helical spring located between respective spigots  117   a ,  119   a ; in an alternative arrangement, the clutch washer can be formed without the spigot  117   a  or omitted altogether, the spigot  119   a  can be omitted and the spring could be a resilient cylindrical rubber material or, in yet a further alternative arrangement, the spring in the form of a resilient rubber material could be integrally formed with the ground-contacting ferrule, as an insert neck thereof in the lower end of the sleeve  113  and bearing on clutch plate  117  or directly on the lower face of the plunger  112 .