embodiments of apparatus according to the invention will now be described in detail by way of example only with reference to the accompanying drawings in which : fig1 shows a first embodiment of a pipe extrusion line for practising the method of the invention in axial cross - sectional view ; fig2 shows a similar view of another embodiment of a pipe extrusion line for practising the method of the invention ; fig3 shows a similar view of a further embodiment of a pipe extrusion line for practising the method of the invention , and fig4 shows an axial cross - sectional view of an embodiment of an injection moulding apparatus for practising the method of the invention . fig5 ( a ) and ( b ) show in diagrammatic form , two embodiments of apparatus according to the invention for the manufacture of a composite metal / plastics pipe . fig6 shows a mechanism to graft ricinoloxazoline maleinate ( oxa ) onto polypropylene . in the drawings the extruder itself is not shown , although in most cases a conventional screw extruder can be used . certain materials with very high molecular weight may require ram extruders ( piston extruders ) or the like instead of conventional screw extruders . also multilayer products can be extruded by means of ram extruders by applying suitable crosshead technology . in fig1 to 3 and 5 , the pipe is radially expanded using a mandrel , which preferably is supported at a first end by the extruder body , for example , by using a support member extending through the extruder screw , and / or optionally at a second end by a calibrator , for example , wherein the mandrel or a support member therefor rests on the solidified wall of the polymeric material extrudate passing through the calibrator . it is important that at least the layer to be oriented preferably is extruded with a tooling system that is totally spider free , e . g . the mandrel is supported upstream of the material flow and hence gives a flow without any weld lines . the need for this is due to brittleness of many glassy state cross - linked polymers . any spiders in the flow of material that has begun to cross - link will have detrimental effects to the hoop strength of the product , and this becomes clearly visible when trying to expand the parison . very effective in minimizing the detrimental effects of weldlines are certain cross - heads with rotating die - sets . a rotating mandrel with counter rotating sleeve can also give a desired fibre orientation in the hoop direction where fibres are added to the plastics material . examples of suitable arrangements can be found , for example , in fi 83184 , gb 2089717 , gb 1325468 , u . s . pat . no . 3 , 244 , 781 , wo90 / 15706 , wo84 / 04070 , ep 057613 , the entire disclosures of which are incorporated herein by reference for all purposes . in fig1 there is fragmentarily shown a die 10 and a fixed core 11 which form part of an extrusion head of a conventional pipe extruder ( ram or screw extruder ) and define an annular die opening . the inner core projects from the extrusion head and forms at its free end a mandrel 11a . an olefin ( co ) polymer material , together with a suitable quantity of cross - linking agent , is plasticized in the extruder and is discharged from the end of the extruder as a cylindrical tubular extrudate 12 having a relatively large wall thickness . at the discharge opening of the extrusion head there is provided a heater 10a such as a radiation heater , for heating the tubular extrudate to a temperature which is sufficient in order to cross - link the material thereof to a degree ranging from 1 to 100 %. downstream of heater 10a there are provided along the path of the tubular extrudate two opposite circulating trains of concatenated mould halves 13 which are moved in an endless path over drive sprockets 14 . along the path of the tubular extrudate the mould halves are guided by means , not shown , to come together at mandrel 11a and to form a bipartite mould forming a cylindrical mould cavity enclosing the tubular extrudate . the mould halves are driven along the path of the tubular extrudate in the direction of movement thereof at the same speed as that of the extrudate . a mandrel 15 is located inside the tubular extrudate and is attached to the extrusion head by means of a bar 16 . through a passage in the bar a gaseous fluid such as air or an inert gas is supplied to the interior of the tubular extrudate in the space defined between mandrel 11a and mandrel 15 in order to keep the wall of the tubular extrudate engaged with the surfaces of the bipartite mould cavities . the mould halves 13 are heated at a suitable location in the endless circulation path thereof , e . g . at 17 , by suitable heating means operating with fuel burners or electric resistance elements . when the extrudate wall contacts the heated bipartite moulds heat will be supplied to the polyethylene material to maintain said material at the cross - linking temperature for a period sufficient to reach the desired degree of cross - linking . downstream of mandrel 15 , a plug 18 , preferably of a balloon type , is provided in the tubular extrudate said plug being anchored to mandrel 15 by means of a rod 19 . pressurized fluid is supplied to the balloon plug through passages in rods 16 and 19 to keep the plug inflated in sealing engagement with the inner surface of the tubular extrudate . in the space between mandrel 15 and plug 18 a pressure is maintained by means of fluid such as air or inert gas supplied to said space through passages in rods 16 and 19 said pressure being higher than the pressure maintained in the tubular extrudate between mandrel 11a and mandrel 15 . the tubular extrudate , which is still soft , will be exposed to free expansion radially allowing hoop stretching of the wall thereof under the influence of this higher pressure to form a tubular member with a larger diameter than that of the tubular extrudate leaving the extruder , and with a wall thickness that is reduced in relation to the wall thickness of said extrudate . outer support rollers 20 , which may be connected to a drive mechanism to improve the process control possibilities , are provided at mandrel 15 to sealingly engage the tubular member against said mandrel , and a calibrator 21 is provided in the path of the tubular member located in a position where the pipe has been expanded . calibrator 21 forms a passage determining the outer diameter of the finished tubular member and provides cooling for the tubular member by the supply of cold water which is distributed over the outer surface of the tubular member through apertures 22 in the surface of the calibrator which is engaged by the moving tubular member . in a further embodiment , the calibrator can be omitted and replaced by a conventional corrugator when a corrugated oriented pipe is to be produced . the cooling of the tubular member is sufficient to solidify the polymer material so that the tubular member when exiting from the calibrator 21 is a rigid pipe downstream of the calibrator . a take - up device 23 is provided which engages the outside surface of the rigid pipe and operates to impart to the pipe axial traction . the speed of the take - up device preferably should be adjustable so that the positive traction force imparted to the moving pipe can be controlled . it should be mentioned that the traction force could also in special cases be negative because the pipe gets shorter during expansion if not drawn . after hoop stretching of the at least partly cross - linked olefin ( co ) polymer material by expansion of the tubular member between mandrel 15 and calibrator 21 and the axial stretching of the pipe effected by take - up device 23 , the finished pipe should preferably have a relationship between wall thickness and diameter which is at least 1 : 100 , preferably around 2 : 100 or greater , for example greater than or equal to 3 : 100 . the hoop stretching of the pipe material causes orientation of the olefin ( co ) polymer material in the hoop direction and this stretching preferably should range from 25 % to 400 % and preferably is around 100 %. the axial stretching of the pipe material preferably should range from 0 % to 400 %, more preferably about 30 %, and causes orientation of the olefin ( co ) polymer material in the axial direction . by the bi - directional orientation of the ( co ) polymer material improved strength is imparted to the pipe , and due to the ( co ) polymer material being at least partly cross - linked when the orientation is effected , such orientation can be effected and maintained in a wide temperature range , typically from 135 ° c . to 250 ° c . further cross - linking can be effected after expansion of the tubular member on the expanded pipe at a position between calibrator 21 and balloon plug 18 . this can be effected , for example , by gamma radiation or electron radiation of the pipe , but preferably is obtained by heating of the extruded pipe at said position , provided that there is a sufficient amount of cross - linking agent left in the material after the initial cross - linking obtained by heating of the ( co ) polymer material in the bipartite moulds . such reheating can be effected by means of circulating trains of heated concatenated mould halves as previously described and subsequent calibration and cooling between calibrator 21 and balloon plug 18 . the further cross - linking after orientation of the ( co ) polymer material can provide increased dimensional stability against reversion of the orientation at higher temperatures . heating of the tubular member immediately downstream of the extrusion head can be dispensed with if the ( co ) polymer material is heated sufficiently in the extruder to be kept at the necessary temperature for a sufficient time for cross - linking to the desired degree to take place before orientation . it should also be understood that other means for holding the temperature of the extruded tubular member or for reheating the pipe , respectively , than heated circulating mould halves , e . g . a heating bath or dielectric heating , can be used . however , circulating mould halves are preferred , for example , in manufacturing oriented ribbed pipes . free radial expansion of the tubular member is used in the embodiment described above , but the expansion can also be effected over a mandrel inside a jacket or similar device surrounding the tubular member as shown in fig2 . the mandrel 11 is supported preferably through the extruder in order to avoid spider legs which leave weak spots in the material which begins to cross - link . the mandrel diameter is kept constant or increases continuously or stepwise until the final expansion starts at mandrel head 11b . it is important that the heat flow from the hot tooling 10 , 11 is prevented from reaching the low temperature area of the apparatus , comprising the extruder and the die entry . if necessary , suitable insulation should be provided . a typical temperature difference between the extruder screw end of the apparatus and the hottest end part of the tooling is 50 deg . c . or more . in the embodiment of fig2 mandrel 11 is extended to form a mandrel head 11b which widens conically in the flow direction of tubular extrudate 12 to expand said extrudate radially so as to stretch the plastics material in the hoop direction . the conical portion of mandrel head 11b joins a cylindrical portion for inside calibration of the pipe formed by expansion of the tubular extrudate . the mandrel head thus has a substantially s - shaped contour . suitable angles of the conical part depend on the extrusion speed . suitable values range from 5 degrees up to 30 degrees . greater angles can easily lead to too fast a deformation speed which will cause the properties of the oriented article to deteriorate . practical usable and preferred deformation speeds range from 0 , 002 to 5 s - 1 . die 10 is extended to form a jacket 10a enclosing the tubular extrudate when passing from the extruder to and over the conical portion of mandrel head 11b . thus , it will be seen that mandrel head 11b and jacket 10a define a space for the radial expansion of the tubular extrudate passing therethrough . the surfaces defining said space can be coated with a low friction material such as for example polytetrafluoroethylene . in this embodiment , the jacket of fig2 can end close to the point where the conical portion begins . in this case speed controlled rollers could be provided in the vicinity of mandrel head 11b . jacket 10a can be provided with electric heating elements on the outside thereof for heating the tubular extrudate as may be necessary in order to impart to said extrudate the temperature necessary for the desired cross - linking to take place when the tubular extrudate is passing through the jacket . further cross - linking in this case can easily be achieved by extending the heated length of mandrel head 11b . furthermore , the end part of jacket 10a can be cooled in order to give a shiny outside to the pipe and for the purpose of locking ( preventing ) excessive die swell . also mandrel head 11b can be heated over the conically widening portion thereof and can be cooled downstream of said portion with a series of different cooling circuits . cooling is needed to freeze the orientation but also because of the good surface finish it gives to the inside of the product . throughout the process avoiding stick - slip flow is critical and correct temperatures of the sliding surfaces are essential to keep them slippery . an optional bar 19 is connected to mandrel head 11b and anchors balloon plug 18 to the extruder , said head being located at the entrance end of take - up device 23 . as in the embodiment previously described there are in bar 19 passages for supplying a gaseous fluid such as air or inert gas under pressure to balloon plug 18 and to the interior of the pipe formed after expansion of the tubular member . between mandrel head 11b and balloon plug 18 there are provided nozzles 24 for sprinkling cooling water over the pipe both when it passes over the cylindrical portion of mandrel head 11b and when it has left said portion in order to rigidify the calibrated pipe . the benefit of the mandrel process described that it can easily be used for both internally calibrated pipes ( cooling extension of mandrel head 11b ) and for externally calibrated pipes ( with a similar arrangement as in fig1 ). the need for plug 18 depends partly also from the lubrication system . in a preferred embodiment the pressurized fluid between plug 18 and mandrel head 11b , which can be used for forcing the still soft member against an outside calibrator , can function as a lubricant , at least for the start - up phase , between the inside of the member and the outside of the mandrel and the plug , respectively . the cross - linking process can be initiated already at the end of the extruder , for example , inside die 10 , by any suitable means , e . g . uv , if die 10 is made of glass . also , radiation or electron beam cross - linking can be used . then , the main part of cross - linking is carried out in the die or the bipartite moulds . the exact point where cooling of the member starts after expansion should be chosen with regard to the desired cross - linking in the expanded state . a long hot section in the mandrel head 11b serves the function of secondary cross - linking of the product in order to enhance its dimensional stability . known processes for stretching of plastic pipes , e . g . the process disclosed in de 23 57 210 , most often include a fairly long conical mandrel . in order to achieve high orientation rates shorter conical parts might be interesting . on the other hand , if the orientation takes place freely i . e . by means of a differential pressure over the wall of the tubular member , then said member can adopt an s - shaped curve , which is illustrated in ep 0563721 , where it is used for free expansion after the die , the cross - section being close to inverted hyperbolic or parabola shape . this shape is often seen in film blowing , and results from a balance of modulus , drawing speed , temperature , wall thickness and draw ratio . surprisingly , this shape is also effective as a form of mandrel in the closed die system of the present invention as illustrated in fig3 . without wishing to be bound by any particular theory , it is believed that the optional hydraulic lubricating agent , which can be injected at both sides of the tubular member , forms with this shape a natural , well balanced hydrodynamic cushion . the benefit of this form is that the likelihood of the material dragging on the mandrel is reduced . this has been found beneficial also where no lubricating agents are used but stable plug flow is achieved with coatings or by the use of internal lubricants . the tendency of high molecular weight material to flow in a so - called &# 34 ; slip - stick &# 34 ; fashion should be minimised as far as possible . in an analysis of extruded pipes , it has been observed that unsatisfactory pipes almost invariably show a flow pattern on their surfaces ( not visible to the naked eye ) which a fourier transform analysis reveals to have an amplitude of 0 . 8 mm or more . in satisfactory pipes , with a steady plug flow in the tooling , no such pattern is found . in these cases , coatings which have good lubricity properties , for example , polytetrafluoroethylene , can be adequate . low friction in the cavity area is important for the process to work . very good results have been obtained using a cavity having a rough metal surface which has a diamond like surface ( dlc ), in which any irregularities have been filled with teflon . liquid coatings can be used but generally are of very limited endurance . hydraulic lubricating agents , for example , silicone - oil or glycol can however give excellent results . also , internal lubrication of the polymer material can be effective . suitable internal lubricants depend on the material to be processed but for example acuflow ( trade mark ), fluorinated rubber compounds such as viton ( trade mark ) and dynamar ( trade mark ) can be used . fig3 shows an extrusion line wherein the polymeric material is oriented or aligned in the thermoplastic state prior to cross - linking and final orientation . a conical extruder 31 , for example as described in ep 0422042 , is illustrated schematically . this extruder can permit the support of a mandrel through the extruder as preferred in certain embodiments of the invention . in addition , the extruder can produce a multiple layered product if desired . other suitable extruders can , of course , be used as appropriate . 33a and 33b represent schematically different material feeds to the extruder , and 32 is a rotating double screw . through the extruder , a hollow shaft 42 is connected to a mandrel 41 . axial movement of the shaft can be adjusted by means of a nut 44 . the temperature of the material in the extruder is kept below the reaction ( cross - linking ) temperature up to the extruder orifice 43 . after the outlet 43 the polymeric material 34 enters a cavity means 35 defined by the mandrel 41 and an outer jacket 48 . in this section , the diameter of the mandrel 41 is increased in order to orientate the molecules of the polymeric material . initially , however , the temperature is still kept substantially below the reaction temperature . at around the mid - point of the mandrel 41 , or towards the end of its conical section , the temperature of the polymeric material is raised using the heaters 46 around the surrounding outer jacket 48 . further , or alternatively , heaters may be positioned inside the mandrel 41 ( not shown ). any suitable heating method may be used , for example the outer jacket may comprise sections of material transparent to ir or rf radiation from suitable heating sources . in this heated section the reaction begins . the reaction time can be determined by the length of a cylindrical second part of the mandrel 41a . in some cases the cylindrical part 41a can be omitted or replaced by a section having a smoothly increasing or stepwise increasing diameter . the polymeric material exits the discharge orifice 35a of the cavity means and enters the inlet end 36a of the die orifice 36b of the extruder die 36 . the extruder die 36 contains the final orientation mandrel 45 , which is connected to the mandrel 41 and is also heated . the mandrel 45 has a smoothly increasing diameter , and a curved , substantially parabolic outer surface as shown . alternatively , the entire conical die could also be smoothly conical with increasing diameter from flow area a1 to flow area a3 , for example , having a cone angle of from about 3 to 30 degrees . the extruder die can also optionally be provided with temperature control means for maintaining in the die orifice an axial temperature gradient descending in the direction of flow through a median die temperature substantially equal to the normal melting point of the polymeric material so that solidification of the polymeric material will be inhibited in the inlet end 36a of the die orifice and may be initiated within the die orifice 36b , for example , towards the die outlet 37 . the heated mandrel 45 is connected to a cooling mandrel 47 which gives a smooth inner wall to the extrudate and also freezes in the orientation produced in the polymeric material . for a similar purpose , the outer jacket 48 is provided with short cooling rings 49 at the die outlet 37 . in the example , the flow area a1 at the extruder outlet is substantially the same as flow areas a2 at the cavity means discharge orifice and a3 at the die outlet , and this configuration , in which there is substantially no increase in the cross - sectional area of flow , is preferred . in certain cases , however , the areas a2 and a3 can be smaller than a1 . in general , the flow areas a2 and a3 are from 0 . 9 to 2 . 0 times the area of a1 . preferably the arrangement is such that the oriented polymeric material is constrained against its natural tendency to lose its molecular orientation by radial swelling . when the polymeric material leaves the die outlet 37 ( at a3 ) there may still be some cross - linking proceeding . this can be beneficial as it can reduce any tendency to shrink back . after leaving the die outlet 37 , the extruded polymeric pipe contacts the cooling mandrel 47 and from the cooling mandrel , the polymeric pipe enters a calibration sleeve 50 . within the calibration sleeve 50 , or in the vicinity thereof , the pipe can be supported with a balloon type plug ( not shown ) for the purpose of inducing fluid pressure against the calibration sleeve . in order to reduce friction against the calibration sleeve wall water lubrication can be used . the calibration sleeve itself can have a serrated internal surface which can be coated , for example , with a friction reducing coating such as teflon or diamond . the haul off and cooling tanks of the apparatus are of conventional design and are not shown in the drawing . fig4 shows on example of a suitable set up for the injection moulding of cross - linked oriented plastics pipe bends . the injection moulding apparatus 60 comprises a body 66 , surrounding a mandrel 61 , 62 , 63 , in three sections . the first section 61 of the mandrel provides the non - oriented inner dimension of the pipe bend . the second section 62 is a heated conical section whereby the plastics material is radially expanded and oriented . the third section is a heated cylindrical section whereby further cross - linking of the plastics material can take place . the plastics material resides in passage 64 , between the body 66 and the first section 61 , and is conveyed by the action of the extruder screw ( not shown ) to the passage 67 , via the conical passage 62a , between the body 66 and the mandrel section 62 , in which it is oriented and cross - linked . the oriented and cross - linked plastics material received in the passage 67 is then forced by the action of the sleeve piston 65 ( shown in its retracted position ) into the injection mould 70 . the mould has an &# 34 ; end gate &# 34 ; type opening 72 into the mould cavity 68 , and has a core 69 . as illustrated the mould also has a pipe bend socket section 71 , which can be provided with a collapsible core ( not shown ). a similar apparatus can be provided , in accordance with the invention , for producing an oriented blow moulded product . in this case , the mandrel section 63 , the core 69 and the collapsible core of the socket section 71 can be replaced by a pressurisable fluid . examples of further extrusion apparatus and articles produced thereby which can advantageously be used in and produced by the method of the present invention are described and claimed in our copending international patent applications nos . pct / fi96 / 00261 and pct / fi96 / 00359 , the entire disclosures of which are incorporated herein by reference for all purposes . in fig5 ( a ) and ( b ) there are shown in fragmentary diagrammatic cross section two devices for the manufacture of a metal / plastics composite pipe . in fig5 ( a ) an extruded cross - linkable parison 80 issuing from an extruder die outlet 81 is pressed against a metal pipe 82 by means of a conical heated mandrel 83 . the heated mandrel raises the temperature of the parison to the cross - linking temperature and at the same time orients the plastics material of the parison by giving it a diametral draw . the metal pipe is formed by helically winding a metal strip and welding or mechanically interlocking the lateral edges 84 of the strip . the metal pipe can be transported at the same speed as the extrusion speed , or faster , if it is desired to impart an axial draw to the plastics material . fig5 ( b ) shows an alternative device in which an oriented plastics pipe 90 is formed by extruding a cross - linkable parison of plastics material from an extruder die 91 , and cross - linking and simultaneously imparting a diametral draw to the plastics material of the parison by means of a conical heated mandrel 92 . an outer metal or fibre reinforced plastics sleeve 94 is formed over the oriented plastics pipe by helically winding a strip 93 of metal or ( fibre reinforced ) plastics material of any suitable cross - section therearound . the crystalline or semi - crystalline thermoplastic polymeric material can be , for example , an olefin ( co ) polymer which throughout this specification includes olefin homopolymers , copolymers or melt blends of two or more ( co ) polymers which either inherently or as a consequence of melt blending have the desired haul - off - tension , molecular weight and molecular weight distribution characteristics . preferably the olefin ( co ) polymer to be extruded should have a density which is at least 900 kg / m3 , more preferably above 920 and most preferably from 930 to 960 kg / m3 . the definition of polyethylene in this context includes copolymers of ethylene with at most 5 % by weight of an alkene - 1 with 3 or more carbon atoms . in a preferred embodiment as described below the material is hd polyethylene with the addition of organic peroxides as cross - linking agents for cross - linking during extrusion , and phenolic antioxidants . preferably the additions of peroxides and antioxidants are each in total from 0 . 1 - 1 . 5 % by weight of the polymeric material , preferably 0 . 3 - 0 . 5 %. generally , the material to be crosslinked or vulcanized can be any crosslinkable extrudable material such as polyolefins , ethylene copolymers , vinyl polymers , polyamides , polyesters , polyurethanes , fluorinated polymers or co - polymers , and elastomers , in particular ethylene - propylene elastomers and some synthetic rubber compounds . preferably the orientable crystalline or semi - crystalline thermoplastic polymeric material is a semi - crystalline polymer such as polyethylene , polypropylene or polyvinylidene fluoride , an amorphous crystallizing polymer such as polymethylmethacrylate or a crystallisable polymer such as polyvinylchloride , polyesters or polycarbonates . the starting materials can be in granulate or powdery form . useful polymers or comonomers which can be blended with the orientable thermoplastic polymeric material matrix ( especially a polyolefin matrix ) prior to extrusion in order to improve the properties of the oriented end product include , for example , ethylene vinyl acetate , epdm - terpolymers , polybutadienes , copolymers of isobutylenes with conjugated dienes , mono - and polyfunctional acrylates and methacrylates , paraffin waxes , maleinates , especially ricinoloxazoline maleinate ( oxa ), maleinanhydride , styrene etc . typical cross - linking agents are different peroxides such as dicumyl peroxide and certain dimethacrylates and azo compounds . also silanes can be used as cross - linking agents for cross - linking of material sections of the finished product in a water oven . for the outside of the product also cross - linking by irradiation or photoinitialized systems are available . whichever cross - linking process is used , it may be advantageous to incorporate one or more co - curing agents for example polyunsaturated monomers such as triallyl cyanurate , diallyl phthalate , benzoquinone and ethylene glycol dimethacrylate . the cross - linking agent is preferably added to the polymeric material in an amount of at least 0 . 01 % by weight , more preferably from 0 . 1 to 5 % by weight , most preferably from 0 . 1 to 1 . 5 % by weight , for example from 0 . 3 to 0 . 5 % by weight . by the addition of fillers such as fibres or flakes ( e . g . mica ) in the cross - linked layers and in the non cross - linked layers or in some layers only , for example , the heat deflection temperature ( hdt ) of the product can be increased . any suitable discontinuous fibre may be used . fibres which reinforce matrices generally include fibres having an average aspect ratio of 10 - 3000 . various types of organic and inorganic fibres are suitable either in monofilament or stranded form . illustrative examples of satisfactory discontinuous fibres include polyamide , rayon , polyester , glass , asbestos , stainless steel , carbon , wollastonite and ceramic whiskers . typical loading levels are from 10 to 30 %. examples of useful laminar fillers include mica , talc and graphite flakes . chalk , silica and fly ash may also be included . the amount of filler or fibre which may advantageously be included depends on the nature of the filler , but up to 50 % may usefully be incorporated . especially useful fillers are , for example , those that make the polymer conductive such as carbon black , react to dielectric heating methods such as induction or microwave heating or are ( ferro ) magnetic by nature . the reader &# 39 ; s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification , and the contents of all such papers and documents are incorporated herein by reference . all of the features disclosed in this specification ( including any accompanying claims , abstract and drawings ), and / or all of the steps of any method or process so disclosed , may be combined in any combination , except combinations where at least some of such features and / or steps are mutually exclusive . each feature disclosed in this specification ( including any accompanying claims , abstract and drawings ), may be replaced by alternative features serving the same , equivalent or similar purpose , unless expressly stated otherwise . thus , unless expressly stated otherwise , each feature disclosed is one example only of a generic series of equivalent or similar features . the invention is not restricted to the details of the foregoing embodiments . the invention extends to any novel one , or any novel combination , of the features disclosed in this specification ( including any accompanying claims , abstract and drawings ), or to any novel one , or any novel combination , of the steps of any method or process so disclosed .