referring first to the preferred embodiment of fig1 - 10 , the assembly 30 includes a screw 31 having a hexagonal head 32 at one end and a gimlet point or tip 33 at its opposite end from which a uniformly threaded portion 34 extends to an unthreaded shank portion 35 that extends from the head 32 . an expandable coil 36 is assembled on the tip 33 and extends outwardly therefrom . a cylindrical spacer 37 is assembled on the unthreaded shank portion 35 of the screw 31 . the coil 36 of the preferred embodiment is illustrated in fig8 and 10 . it has an enlarged loop 38 at one end slightly larger than the nominal thread diameter of the screw 31 , with a tip 39 projecting laterally outwardly to score or scrape the sidewall of a predrilled hole 40 of a concrete or masonry structure 41 . this projecting tip 39 prevents the coil 36 from rotating when the screw 31 is torqued to advance into and expand the main loops 42 of the coil 36 . this projecting tip may be of any configuration which will bear against , or into , the wall of the hole 40 sufficient to prevent rotation of the coil 36 . by the time the screw 31 has been rotated an eighth to a quarter turn into the coil 36 the coil will be permanently fixed and prevented from rotating . a projection could also be utilized at the other end of the coil 36 or at some location intermediate the length of the coil to perform this same function . the pitch of the enlarged first loop 38 of the coil 36 should preferably be equal to the pitch of the thread of the screw 31 . the main loops 42 of the coil 36 are formed with a pitch diameter smaller than the nominal pitch diameter of the threads of the screw 31 . the inside diameter of these main loops 42 may be from 50 % to 60 % of the thread root diameter of the screw 31 . the spacing between successive main loops 42 may be between 15 % of their wire diameter to 33 % of the wire diameter . but the pitch of the main loops 42 should not exceed the pitch of the mating screw threads . these proportionate dimensions will allow the screw thread pitch and the coil loop pitch to remain in parallel helical alignment while the coil 36 is being expanded from the unexpanded configuration ( fig1 and 2 ) to an expanded configuration ( fig3 - 5 ) in the sidewall of the hole 40 . the enlarged loop 38 will allow the coil to be preassembled to the gimlet point 33 of the screw threads and turned to tighten enough to be retained thereon . the main loops 42 of reduced diameter will permit the leading edge of the progressing screw thread to slice between the loops ( fig3 and 4 ) to begin expanding the coil 36 into its expanded configuration ( fig5 ). while main loops 42 are being progressively expanded the unexpanded loops are free to wiggle about in a clockwise direction , first touching one side of the hole 40 , then the other as the leading thread of the screw slices between and opens the space between loops to conform to the screw thread pitch , thus reducing the possibility of cross threading occurring during installation . it has been found that wire coil loops originally spaced apart to conform to the spacing of the screw thread pitch and diameter are unreliable in preventing cross threading . any deformity to that kind of wire coil while it is being inserted into a hole , during shipping or during handling , can cause an unparallel helix angle alignment , or a coil with greater pitch distance than the screw threads , either of which may produce cross threading . only a coil which is expanded from undersize to the screw dimension by a rotating screw will reliably avoid cross threading . the number of loops in a wire coil has a definite effect on the resulting holding power , or resistance to pull - out , of a concrete anchor of the wire coil / screw thread type . the more wire coil loops engaging corresponding screw threads the stronger the resistance to pull - out . thus , a coil can be produced that will develop the full strength of the anchor screw or develop the full strength of the concrete . by simply using enough loops and engaging an equal number of screw threads in a hole of correct depth , load testing will either break the screw or break the concrete rather than the coil . it is therefore one object of this invention to provide means whereby a previously set , or installed , anchor may be reinforced to develop greater holding power after it has been initially installed , if it is desired to increase the safety factor . the spacer 37 of the embodiment of fig1 - 10 is illustrated in fig6 and 7 . this spacer 37 is generally tubular and dimensioned to fit , as previously mentioned , on the unthreaded shank portion 35 of the screw 31 . for this purpose , it is formed with a longitudinally extending slot 43 throughout its length , which permits the spacer 37 to pop off the screw 31 when it is compressed between the head 32 of the screw 31 and the concrete structure 41 or a mounting plate 44 , such as a foot plate of machinery to be secured to the structure 41 . this slot 43 also can serve to permit assembly of the spacer 37 onto the unthreaded shank portion 35 of the screw 31 by opening the spacer 37 at the slot 43 , which may be a desired manner of assembly in a procedure where the coil 36 is first assembled on the screw 31 before the spacer 37 is attached . fig1 - 20 illustrate an assembly 45 utilizing the same type of screw 31 and coil 36 as in the embodiment of fig1 - 10 , but the spacer 46 in this embodiment has one end 47 of its slot 48 flared for ease of assembly on the screw 31 . the spacers 37 , 46 are of material rigid enough to be retained about the shank portion 35 of the screws 31 and resilient enough to pop off the screw 31 when subjected to compressive forces as the screw is torqued . obviously , the spacers 37 , 46 provide an indication of the depth of insertion of the screw 31 and coil 36 into the hole 40 of the concrete structure 41 without requiring sighting of a marking or other determination of the depth of insertion . other configurations of spacers may be utilized to provide the purposes described . as the diameter of the screw 31 is controlled at the time of manufacture and the diameter of the hole 40 is controlled by the drill bit diameter which is controlled by diameter tolerance standards which are adhered to by the masonry drill bit manufacturers , the only unknown diameter dimension to be considered is the preformed hole diameter through the fixture or machinery mounting plate 44 which is to be anchored to the concrete structure 4 . therefore , to prevent the spacer from being forced into the mounting plate hole so that it will not pop off the screw shank 35 when it is compressed by the underside of the screw head 32 during torquing , the wall thickness of the spacer or fins , flanges , or spool shapes , or other projections may be utilized to span any gap between the screw 31 and the hole of the mounting plate 44 . in fig6 and 7 the spacer 37 is formed with exterior radially projecting , longitudinally extending ribs 49 that also provide a strengthening function . these ribs or other projections or the thickness of the spacer also can be utilized to support a washer 50 pre - assembled between the spacer 31 and the head 32 of the screw 31 to prevent a deep driving socket 56 ( fig1 - 20 ) from seating over the end of the spacer and thereby preventing the spacer element from popping off the screw 31 . fig1 - 5 illustrate in series the procedure involved in inserting and expanding a coil 36 in a hole 40 in a concrete structure 41 . this procedure may be followed whether the coil is to be used to serve for attachment of an overhead anchor , or of an anchor in a floor , in a wall or in an edge application . fig1 illustrates an assembly 30 of a headed screw 31 , a washer 50 held against the underside of the head 32 , a spacer 37 and a wire expansion coil 36 retained on the gimlet point 33 of the screw 31 . fig2 illustrates the assembly 30 partially inserted in a pre - drilled hole 40 and through a flange of a mounting plate 44 which is to be secured to the structure 41 . at this location the assembly 30 has been tapped in axially until the spacer abuts the mounting plate 44 and the screw head 32 , at which position the spacer 37 yieldably resists further insertion of the screw , indicating to the operator that the screw is in proper position for the coil 36 to be expanded into the wall of the hole 40 . fig3 illustrates the screwing or torquing of the screw 31 into the coil 36 to partially expand the coil 36 with the spacer beginning to deform under an imposed compressive force caused as the screw is torqued and advances axially into the coil 36 and hole 40 . fig4 illustrates a fully and completely set screw or anchor . the spacer 37 has by now popped off and the gimlet point 33 with its reduced diameter lead screws now project through the expanded wire coil 36 . fig5 illustrates the coil 36 expanded into the wall of the hole 40 after the set anchor screw and washer have been removed , with the coil 36 acting as a permanently inserted screw thread in readiness for the installation of an anchor or for insertion of a second coil at a lesser depth . fig1 - 14 illustrate how a spacer 37 may be used with a hanger - bolt anchor for the suspension of objects such as pipe . a full description of the installation and removal of hanger bolt anchors may be found in u . s . pat . nos . 4 , 536 , 115 and 4 , 635 , 337 . in fig1 , a spacer 37 has been positioned on the shank 35 of a screw 51 against one end of a coupling nut 52 threaded on machine screw threads on the outer end of the screw 51 . a hex headed bolt 53 has machine screw threads 54 engaged with the internal machine screw threads in the opposite end of the coupling nut 52 until the machine screw threads of both the screw 51 and bolt 54 meet and bear against each other inside the coupling 52 , thus providing a means for torquing the entire assembly to effect the setting and expansion of the wire coil 31 . in fig1 , the spacer 37 is being deformed while the bolt and screw assembly is being torqued in order to set and expand the wire coil 36 . further torquing will cause the spacer 37 to pop off its position on the shank 35 of the screw 51 . it then has completed its purpose . in fig1 , the screw 51 has been completely set , the wire coil 36 fully expanded and the bolt 54 has been replaced with a pipe yoke 55 to support a pipe . in fig1 , the entire hanger bolt assembly including a pipe yoke 55 has been removed , leaving the expanded coil 36 in place as a permanent threaded insert ready for the installation of an anchor or another wire coil , or for application of a sealing compound , if desired , or for permanently plugging of the hole if , for example , the hanger bolt assembly is no longer needed , or the pipe line has been re - routed . fig1 - 20 illustrate the sequence of assembling the spacer 46 of the type illustrated in fig1 . in this embodiment the spacer 46 has a flared end slot 48 that facilitates mounting on a screw 31 that already has a coil 36 assembled thereon . these figures then show the procedure for inserting the assembly 45 into the structure hole 40 axially until the spacer 46 stops the insertion of the screw 31 in proper location for positioning the coil 36 at a desired depth within the structure hole 40 ( fig1 ). the screw 31 is then rotated by engagement of the socket 56 of a drive tool on the hex head 32 of the screw 31 and against the washer 50 . one of the features of the present invention is the use of the coil inserting and expanding assembly and method to insert and expand two or more spaced coils within a hole of a concrete structure to add attaching strength for mounting of an anchor and to provide tension / compression neutralizing attachment . this is illustrated in fig2 - 25 , wherein a first coil 57 has been inserted in a hole 58 in a concrete or masonry structure 59 in the manner described above . after the insertion of this first coil 57 , two spacers 37 of the type described above with regard to fig1 - 10 are assembled on the screw 31 with a second coil 60 assembled on the gimlet point of the screw 31 and a washer 50 is disposed between the spacers 37 and the head 32 of the screw 31 . as illustrated in fig2 , the two spacers 37 now limit the axial insertion of the screw 31 , with the second coil 60 thereon , into the hole 58 , with the second coil 60 being spaced from the first coil 57 . as illustrated in fig2 , the screw 31 is then torqued to screw it into the second coil 60 , thereby compressing the spacers 37 . fig2 illustrates the screw 31 torqued fully into the hole 40 until the washer 50 seats on the mounting plate 44 . by this time , the spacers 37 have popped off the screw 31 . during this screwing or torquing of the screw 31 the screw expands the second coil 60 into a permanent threaded disposition in the hole 40 and continues to advance into the first coil 57 to facilitate alignment of the threads of the first and second coils sufficiently for threading of an anchor bolt therein . fig2 illustrates the screw 31 being removed from the hole 40 , leaving the first and second coils 57 , 60 expanded and embedded in the wall of the hole 40 for receipt of an anchor bolt . an alternate method of setting multiple coils is to place the first coil into the pre - drilled hole using the screw with one spacer , then withdraw the screw without expanding the wire coil . then place a second coil on the end of the gimlet point of the screw and place two spacers on the shank of the anchor screw , inserting this assembly into the pre - drilled hole until the first spacers stop further penetration . the screw may then be torqued to expand the wire coil nearest the surface , and continuing to turn the screw until the screw engages the inner wire coil and expands it also . there are several reasons why the added reinforcement of a second coil may be desirable . one reason may be that a slab of concrete has not developed the strength that it was designed for . the strength of the anchorage may accordingly be increased to safely handle the expected load by inserting two coils . another reason may be that a machine may develop more vibration than was expected such that to reduce the possibility of the anchor loosening under vibration another , or other , coils may be afterwards installed . in this case , while the normal coil is constructed of soft annealed wire , a second coil may be formed of spring wire to lock the anchor against rotating under vibration . it has been found that for ordinary fastenings spring coils are undesirable because , while the lag screw used with a spring coil causes the spring to expand and be partially embedded into the side of the anchor hole wall without undue difficulty , the removal of a screw from a spring coil is very difficult because the spring wire loops tend to constrict and squeeze the thread root diameter of the screw when an attempt to unthread the screw from the spring wire coil is made . this squeezing of the thread root of the screw threads thereby successfully locks the anchor in place , but the removal of such an anchor is very difficult and damages the screw threads , or the spring coil cuts its own thread impression into the wall of the anchor hole while being backed out , and afterwards the anchor and anchor hole are unusable . however , it has also been found that if a resilient coil made from plastic such as nylon is used as single or multiple coils the screw may be removed from the anchorage without damage to the screw threads or hole . the screw may again be reused in the same expanded element without sacrifice to the original integrity of the fastening . the resilient nylon coils produce less resistance to anchor pull - out than metal coils , but the resistance of the fastening to loosening under vibrating light loads is increased . another important reason for using multiple coils to reinforce an anchorage is that an anchoring coil may be placed in both the tension and compression zones of a concrete slab and be thereby better enabled to resist the stresses imposed by shifting , unexpected , large moving live loads , during periods of stress reversal , or in regions of contraflexure , guaranteeing that in any event at least one anchoring element will remain in a compression zones as tension zones are always potential danger zones for ordinary mechanically expanded concrete anchors . to install multiple anchor coils on both sides of the neutral axis of floor and roof slabs does not require excessively deep anchor holes with the present invention . generally the thickness of such slabs conforms to a formula which states that the perimeter of the slab , in inches , is to be divided by 180 to determine minimum thickness of reinforced slabs . in other words , a slab which measures 20 feet by 20 feet between supports would have a perimeter of 12 inches by 80 feet , or 960 inches . when divided by 180 a slab of 5 . 33 inches thick is indicated , which , in a practical manner , indicates a slab which probably would not exceed 6 inches thick . since the neutral axis of such slabs is usually found near the center of the slab , a hole depth of 31 / 2 inches to 4 inches is indicated for such a slab , for the installation of anchors with expansion elements in both the compressive and tension zones . the series of installations illustrated in fig2 demonstrate anchor installations using single and multiple coils in relationship to the neutral axis na of a typical floor slab . ( for clarity , no reinforcing steel is shown , reinforcing steel being a separate engineering consideration of no significance to this invention .) the first installation from the left in fig2 is a hanger bolt anchor assembly 61 with a pipe supporting yoke 62 attached to the machine screw threaded end of the bolt 61 . two wire coils 36 are expanded in place , one above the neutral axis ( na ) in what is usually a compression zone ( cz ) and a second below the neutral axis ( na ), in what is usually a tension zone ( tz ). the second installation 63 from the left in fig2 is of the type previously described with reference to fig1 - 10 with the coil 36 set in the compression zone ( cz ) above the neutral axis ( na ). similarly , the third installation is in the form of a hanger bolt anchor 64 with a pipe supporting yoke 65 installed in the manner shown in fig1 - 14 with the coil 36 located in the tension zone ( tz ) below the neutral axis ( na ). the fourth installation is in the form of a hanger bolt anchor 66 with a pipe supporting yoke 67 and a single coil 36 extending across the neutral axis ( na ) and being disposed in both the compression zone ( cz ) and tension zone ( tz ). a longer than normal wire coil may be used in this installation for effective extension into both zones . the fifth installation is in the form of an elongated anchor 68 installed similar to that illustrated in the second installation , but extending sufficiently to position two coils 36 , one in the compression zone ( cz ) and one in the tension zone ( tz ) with the neutral axis ( na ) therebetween . the sixth installation is in the form of an anchor 69 having an attached pipe supporting yoke 70 with three coils 36 . the first coil is set in place well above the neutral axis ( na ) in the compression zone ( cz ). the second coil is set astride the neutral axis ( na ) for additional reinforcement in both the compression zone ( cz ) and the tension zone ( tz ). the third coil is set below the neutral axis ( na ) in the tension zone ( tz ). the use of coils on both sides of a neutral axis ( na ) ensures that regardless of shifting and unexpected live loads one coil will always be in a compression zone . even if a shifting or unexpected live load never occurs , the utilization of multiple coils increases an anchor &# 39 ; s resistance to pull - out , with a proportionate increase in resistance to loosening under vibration . fig2 , 28 and 29 illustrate a method of sealing a lag screw , wire coil and hole against penetration of liquids that freeze and thaw with consequent damage , or rusting , to the anchor , or base material into which the anchor is installed , or against penetration be deleterious gases or fumes , or the colonization of bacteria or vermin where fixtures are to be installed in areas where sanitary conditions must be maintained , such as in food processing or pharmaceutical production . in fig2 , a through - set anchor is shown in partial cross - section . a hex headed lag screw 80 is set in a hole 81 with an expanded wire coil 82 in a manner as described above with reference to fig1 - 10 . in fig2 , the lag screw 80 has been removed leaving the expanded wire coil 82 in place , then a caulking compound 83 of any type suitable for the application at hand is injected into the hole 81 . then , as illustrated in fig2 , the lag screw 80 is reinserted and torqued to tighten , thus causing the caulking compound 83 to be injected into every crack , crevice , pore or fissure existing within the walls of the hole 81 , and extruding out the mouth of the hole 81 flowing under the head 84 of the screw 80 and around the washer 85 , or fixture , and effectively sealing the anchorage against entry by foreign matter . the reason that other types of through - set anchors cannot be successfully caulked in place is that threads , sleeves , wedges , etc ., fit too closely together in the hole and there is no way to apply the pressure necessary to force the caulking compound through these tight - fitting components and be injected into every opening , pore , or crack , or extruded out the mouth of the hole because in setting other types of through - cut anchors they are pulled outward , creating cavities , not filling cavities as is necessary to properly seal a hole . in contrast , the pressure created by an inward advancing screw as with the present invention causes the pressure necessary to fill all cavities with caulk and then overflow the hole . it will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of a broad utility and application . many embodiments and adaptations of the present invention other than those herein described , as well as many variations , modifications and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the foregoing description thereof , without departing from the substance or scope of the present invention . accordingly , while the present invention has been described herein in detail in relation to its preferred embodiment , it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention . the foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments , adaptations , variations , modifications and equivalent arrangements , the present invention being limited only by the claims appended hereto and the equivalents thereof .