the fixing devices shown in fig1 and 3 are designated generally by the reference numeral 1 ( and the same applies to fig8 ). in the figures , like parts are designated by like reference numerals . the fixing device shown in fig1 comprises ( and similar in fig8 ) a steel shank 2 of solid right circular cylindrical configuration comprising a top section 3 and a bottom or bone - entry section 4 . bottom section 4 has a groove 5 formed in the surface of the blank shank by cold thread rolling . groove 5 has a helical configuration and extends spirally around the circumference of the bottom section 4 of shank 2 and is co - extensive longitudinally with that section . groove 5 is defined between two parallel marginal ridges 6 and 7 ( one of which is absent in favour of one ridge and a deeper groove in the case of fig8 ), formed of shank material displaced from the groove 5 by the plastic deformation which occurs during thread rolling . top section 3 of shank 2 is formed with a conventional male screw thread 8 to enable threaded engagement of articles to the fixing element 1 when the fixing element 1 is secured in a masonry structure . the axial extremities of the shank 2 are formed having regard to the practicalities of the fixing device 1 in use . thus , for example , the extremity or the bottom portion 4 of shank 2 has a frustoconical configuration to assist bore entry of that extremity . the extremity of the top portion 3 of shank 2 has a domed configuration and is provided with a screwdriver engagement slot , cross - recess , hexagon or square drive ( not shown ) or screw head enlargement such as one configured with a countersink . it will be noted that a land 9 is provided between the turns of the ridge - groove - ridge configuration . in the embodiment shown in fig1 the land has a width between turns as measured axially of the shank 2 of 7 mm . the shank land diameter in the example depicted is 10 . 4 mm and the pitch of the groove 5 is 11 mm , the helix angle of the spiral being 25 °. the groove depth relative to the land level is 0 . 5 mm and the ridge height relative to the land level is 0 . 5 mm . of course , fixing devices conforming generally to the embodiment described may be configured with different values for one or more of the above parameters ( e . g . land width 10 mm , groove pitch 11 mm , helix angle 30 ° and ridge height 1 . 0 mm ). turns 6 ( a ) and 7 ( a ) of ridges 6 and 7 are configured by means not shown to provide a self - tapping capacity in a masonry structure . the fixing device embodiment shown in fig2 is broadly similar to that shown in fig1 . however , in this embodiment the thread represented by the ridge - groove - ridge turns is much coarser and the in - bore extremity of the shank 2 is slotted by means of slot 10 to provide for self - tapping . the device of fig2 is preferred over that of fig1 . threaded upper section 3 has a flat top provided with screwdriver engagement slot 11 . the remaining features of the fixing device shown in fig2 will be readily understood from the figure itself , in comparison with fig1 like parts being designated by like reference numerals . fig3 a shows diagrammatically a masonry substrate 12 whose surface 13 is performed by a right circular cylindrical bore 14 drilled into the masonry substrate 12 using a low speed power driven masonry drill bit without hammer action ( although , of course , hammer drilling or rotary impact drilling may be adopted as an alternative ). in use of fixing devices according to the invention , the first stage in procedures to install the fixing device in a masonry structure is to drill a bore such as that depicted at 14 in fig3 ( a ). a fixing device according to the invention , such as that shown in fig1 or fig2 of the drawings , is offered up to the bore 14 and its extremity remote from the extremity configured for screwdriver engagement is inserted into the mouth of the bore 14 . the fixing element is then rotated manually number of times until the threads 6 , 7 start to engage by tapping a corresponding female thread in the outer portions of the wall of the bore 14 . this practise is continued until finger turning becomes impractical . a screwdriver is then taken by the operator , engaged with the other extremity of the shank 2 by means of the slot provided for the purpose and further turning effected . the thread represented by ridges 6 , 7 continues with this motion to form its own female thread with gradually increasing extent along the length of the internal surface of bore 14 until all of the bottom portion 4 of shank 2 is received in the bore 14 . this stage is depicted in fig3 ( b ) where it will be seen that a slightly different embodiment of the fixing device according to the invention is shown in place . the fixing element shown in fig3 ( b ) is one having a coarse thread sharper than that shown in fig1 . self - tapping grooves 10 traverse the ridge - groove - ridge configurations providing a thread - cutting facility along the length of the shank 2 analogously to the slot 10 shown in fig2 . tabulated in table 1 below are parameters for three specific examples , respectively , of the fixing devices shown in fig1 and 3 ( b ) of the drawings : table 1______________________________________ dia - groove land groove ridgeem - meter pitch helix width depth heightbodiment ( mm ) ( mm ) (°) ( mm ) ( mm ) ( mm ) ______________________________________fig1 . 4 11 25 7 0 . 5 0 . 5fig2 . 4 14 30 10 0 . 5 1 . 5fig3 . 36 11 25 6 . 7 0 . 5 1 . 0 ( b ) ______________________________________ in table 1 , land width is measured between adjacent spaced ridges axially of the shank . groove depth is measured relative to the level of the land and ridge height also is measured relative to the level of the land . the following specific example is intended to illustrate use and performance of fixing elements according to the invention relative to various prior art fixing devices : a number of fixing elements were tested in brickwork as set out at a to h in table 2 . bores of diameters 8 mm , 10 mm , 12 mm and 14 mm were predrilled in solid brick having a compressive strength of 20 . 5 n / mm 2 ( a to e , g and h ) or of 15 n / mm 2 ( f ) to various depth as recommended by the manufacturer or 5 mm in excess of fixing device length using , for example , a conventional drill bit of appropriate size driven by a slow speed power drill without hammer action ( a hammer action could equally be used ). fixing elements , shorter than the bore depths , of various types and having diametric sizes of 6 mm , 8 mm , 10 mm and 12 mm were then selected as noted in table 2 below and matched on the basis bore / element = 8 / 6 , 10 / 8 , 12 / 10 and 14 / 12 except as stated otherwise . matched elements were then introduced , to extents shown in table 2 , into matched bores . pull - out strengths ( i . e . ultimate tensile strengths ) were then determined by applying calibrated loads axially to the fixing elements in the direction of withdrawal . the results are shown in table 2 and readily demonstrate at least comparable performance as compared to some multi - component devices ( rawlbolt ), whilst as compared to bore liners ( fischer nylon plug , upat ultra plug ) and direct fixtures ( rawl spike ), performance was superior . expansion bolts , of course , risk of substrate rupture and slower speed of installation . table 2__________________________________________________________________________ ultimate hole hole thread shank / embedment tensilefixing da depth dia length depth strength substratedevice mm mm mm mm mm kn type comments__________________________________________________________________________a rawlbolt m6 12 50 m6 45 45 9 . 2 20 . 5n / mm . sup . 2 multi component m8 14 55 m8 50 50 11 . 35 20 . 5n / mm . sup . 2 multi component m10 16 65 m10 60 60 14 . 35 20 . 5n / mm . sup . 2 multi component m12 20 85 m12 75 75 21 . 5 20 . 5n / mm . sup . 2 multi componentb sfs spike 4 . 8 40 4 . 8 32 22 2 . 0 20 . 5n / mm . sup . 2 solid nonekc rawl spike 5 . 0 40 5 . 0 40 32 3 . 6 20 . 5n / mm . sup . 2 solid nonek 6 . 5 40 6 . 5 40 32 4 . 3 20 . 5n / mm . sup . 2 solid nonekd fischer nylon plug s6 6 40 5 30 30 2 . 5 20 . 5n / mm . sup . 2 solid plug & amp ; screw s8 8 55 6 40 40 4 . 1 20 . 5n / mm . sup . 2 solid plug & amp ; screw s10 10 70 8 50 50 4 . 4 20 . 5n / mm . sup . 2 solid plug & amp ; screw s12 12 80 10 60 60 4 . 5 20 . 5n / mm . sup . 2 solid plug & amp ; screwe fisher nylon plug s6 6 40 5 30 30 2 . 2 perforated brick plug & amp ; screw s8 8 55 6 40 40 3 . 0 perforated brick plug & amp ; screw s10 10 70 8 50 50 4 . 6 perforated brick plug & amp ; screw s12 12 80 10 60 60 4 . 7 perforated brick plug & amp ; screwf upat ultra plug u6 6 40 5 30 30 0 . 5 15n / mm . sup . 2 solid plug & amp ; screw u8 8 55 6 40 40 0 . 8 15n / mm . sup . 2 solid plug & amp ; screw u10 10 65 8 50 50 1 . 1 15n / mm . sup . 2 solid plug & amp ; screw u12 12 75 10 60 60 1 . 5 15n / mm . sup . 2 solid plug & amp ; screwg fig2 45 6 . 36 40 30 7 . 0 20 . 5n / mm . sup . 2 solid nonekh fig2 55 10 . 4 50 40 12 . 5 20 . 5n / mm . sup . 2 solid nonek__________________________________________________________________________ referring to fig4 a screw heading station comprises a solid metallic block 15 formed with a right circular cylindrical uniform diameter bore 16 . steel wire 17 passes along bore 16 and is urged until its end abutts against stop 20 . a cut - off knife 19 is mounted for reciprocatory motion radially across the mouth of bore 16 so a to server the wire 17 to form a blank 18 . a transfer finger mounted for reciprocatory motion parallel to that of cut - off knife 19 is provided for transferring cut off blank 18 a stage further in the heading operation as depicted at two points in fig4 in broken lines . at the maximum displacement of transfer finger 21 , blank 18 is disposed in register with a bore 23 in solid metallic block 22 , bore 23 being identical with bore 16 in block 15 except that bore 23 has a blind end represented by the crown of a piston 27 moveable axially of bore 23 to provide for different desired lengths of fixing element . whilst retained by transfer finger 21 , blank 18 is displaced into bore 23 in block 22 by means of a first of two punches 25 mounted for reciprocatory motion in the directions of double headed arrow a shown in fig4 . the mouth 24 of bore 23 is depressed into the body of block 22 and have the configuration of a countersink . the first of punches 25 drives blank 18 fully into bore 23 and produces the partial plastic deformation shown in fig5 ( b ). the first punch 25 is provided with a plane punch face 28 . the second punch 25 is provided with a punch face 28 having a structure 26 disposed thereon for forming in the head of the fixing device a screw engagement depression 29 having a so - called posidrive configuration . the action of the second of the two punches 25 complete plastic deformation of the terminal end of blank 18 to form the head 30 shown in fig5 ( c ). the thread rolling station shown in fig6 and 7 comprises a fixed die 31 and a displaceable die 32 . the two dies are spaced apart to form jaw 33 , the gap there between being equal to the core diameter of the product being rolled . die 32 is displaceable in reciprocatory fashion according to the arrow b shown in fig6 . in use , headed blank 18b is inserted into jaw 33 and thus between the fixed and moving dies 31 , 32 by manual or mechanical means ( e . g . a mechanical feed finger ) as is known in the thread rolling art . the vertical position of the blank in relation to the fixed and moving die is governed by a work rest on which the blank 18b rests prior to introduction to the dies by the feed finger . the operational sequence is for the moving die 32 to move clear of being parallel with the fixed die 31 in the direction of arrow b . blank 18b is then transferred by the feed finger into the work rest and pushed against and between the leading edge of moving die 32 and the back edge of fixed die 31 . the reciprocating action of the moving die 32 then carries the blank 18b between them , during which time the blank 18b is plastically deformed to the face of the dies , as the blank rolls along the faces thereof , to form ridge - groove - ridge convolutions are depicted in fig1 and 3 ( b ); a die groove corresponding to a ridge on the fixing element is shown at 6a and another at 7a ( fig7 a ) whilst ridge 5a corresponds to groove 5 of the fixing element . fixing device production using the die of fig9 is broadly the same as described above for the other die configurations given herein . the angle α will be varied to suit the blank diameter used and the material being rolled , stainless steel and boron steel , to give but two examples , giving rise to different requirements in order to achieve controlled plastic flow of shank material from the body of the device to form the helical thread ridges 6 . by using this die structure , a fixing device can be rolled which maintains a core diameter d1 similar to d2 ( or the same ). however , the land in fact has a helical depression as a result of the rolling action exercised to displace shank material and control its flow through the choice of die configuration . the groove 5 is similarly depressed to a helical centre line between the thread ridges which enclose the groove . as compared to two - part fixing systems , fixing elements according to the invention provide efficiency of installation and greater security of fixture in terms of pull - out strength . as shown in table 2 hereinbefore , pull - out strength performance at least in brick is superior to most expansion bolts and plastics fixings in brickwork . the fixing devices according to the invention produce secure fixture in bores in masonry substrates ranging from brick , light - weight aerated autoclaved cement blockwork and various forms of concrete without the problems associated with expansion bolts due to the risk of rupture of the substrate material . fixing elements according to the invention can also easily be manufactured by the steps of cold forging and thread rolling , bright zinc plating and heat treatment without resort to complex assembly operations such as are normally associated with an expansion bolt . this produces economics in terms of materials and manufacturing costs as well as the economics associated with relative ease of installation .