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FIELD OF THE INVENTION 
     This invention relates to an adjustable anchorage, and relates more particularly but not exclusively to an anchorage for a safety net to be utilised during the construction of a building, the net requiring to be reliably anchored to the lower flanges of I-beams forming the skeleton of the building being constructed. 
     BACKGROUND OF THE INVENTION 
     It is currently common for buildings, particularly larger commercial premises, to be constructed around a three-dimensional skeleton or framework of steel I-beams which serve to support concrete flooring slabs or metal deck flooring. Most of the framework is usually at a considerable height above ground, and consequently falls present a grave risk of death or injury to construction workers. The injury risk from falls is mitigated by the use of a safety net suspended from the I-beams around the edge of a floor level or other work location in the building. In the United Kingdom, parts 1 and 2 of BS EN 1263 govern such safety nets and their deployment. Part 2 of BS EN 1263 directs that safety nets be attached to horizontal beams by passing a securing rope alternately through the edge of the net and around the beam. While such an attachment procedure can securely anchor the net (if diligently carried out), the procedure presents certain problems, including the substantial time required to reeve the rope many times through the net edges and around the beams, converse difficulties in removing the rope to free the net (aggravated by weathering of the rope) and the loss of fall protection due to the need to remove the rope (and net) for the laying of flooring supported on the top edges of the beams. 
     OBJECT OF THE INVENTION 
     It is an object of the invention to provide an adjustable anchorage which is capable, inter alia, of being applied to reversibly anchoring a safety net to a horizontal I-beam or similar article in a rapid and simple manner without impeding access to the upper surface of the I-beam during such use of the anchorage. (It is to be understood that in this specification and its accompanying claims, use of the term “I-beam” not only encompasses beams whose transverse cross-section resembles an “I” with bilateral flanges on the top and bottom edges of its central web, but also encompasses beams having other cross-sections though always with bilateral flanges (or their mechanical equivalent) along or near the lower edge of such other forms of beam). It is a further object of the invention to provide an adjustable anchorage capable, inter alia, of being adjusted for efficient utilisation on I-beams whose lower edge bilateral flanges have respective widths in a wide range of widths 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided an adjustable anchorage comprising first and second hook means each capable of being hooked around a respective opposite edge of a bilateral flange, attachment means on at least one of said first and second hook means for the attachment of an article thereto, and adjustable linking means extending between said first and second hook means for mutually linking said first and second hook means in use of said anchorage with said first and second hook means each hooked around a respective opposite edge of the bilateral flange and for thereupon retaining said first and second hook means against the respective opposite edges of the bilateral flange, with the adjustability of said adjustable linking means allowing effective use of the anchorage on various bilateral flanges having respective widths in a substantial range of widths. 
     Said adjustable linking means preferably has an adjustable length between said first and second hook means. Said adjustable linking means may comprise a strap or web secured at one end thereof to one of said first and second hook means together with clamp means for clamping the strap or web to the other of said first and second hook means at a selected location along the strap or web displaced from said one end of the strap or web. Said adjustable linking means preferably incorporates tensioning means capable of applying tension between said first and second hook means whereby to force said first and second hook means against the respective opposite edges of the bilateral flange in use of the anchorage, and said tensioning means may comprise an overcentre form of said clamp means tending in use to shorten the strap or web between said one end thereof and said selected location thereon. Said adjustable linking means may alternatively comprise mutually interpenetrating tongue and slot means together with latch means functioning to latch the tongue and slot means together at a mutual interpenetration which places the first and second hook means at a selected mutual separation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings wherein: 
     FIG. 1 is an end elevation of a first embodiment; 
     FIG. 2 is an end elevation of a second embodiment; 
     FIG. 3 is an end elevation of a third embodiment; and 
     FIG. 4 is a plan view of the third embodiment from beneath. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, this is a fragmentary end view of an I-beam  10  (only the lower edge being shown), to which a first embodiment of anchorage  100  is attached. As viewed in FIG. 1, the lower edge of the I-beam  10  is formed with a bilateral flange  12 , comprising a right flange  14  and a left flange  16 . The I-beam  10  forms part of the framework of a building (not otherwise shown), and is substantially horizontal at a height above ground level which would make a fall from that height liable to cause serious injury. In order to mitigate the risk of falls, the anchorage  100 , together with several other substantially identical anchorages (nor separately shown), is utilised to suspend a safety net (not shown), as will subsequently be detailed. 
     The anchorage  100  comprises a first hook  102  and a second hook  104 , each formed from thick steel rod or strip that is suitably protected against corrosion. The free end  106  of the first hook  102  is hooked around the right flange  14  of the I-beam  10 , while the free end  108  of the second hook  104  is hooked around the right flange  16 . As shown in FIG. 1, the anchorage  100  is only partially installed, and the hooks  102  &amp;  104  are not yet fully tightened against the I-beam flange  12 . 
     A strip  110  of thick fabric webbing is permanently attached to the non-free end  112  of the first hook  102  (i.e. the end of the hook  102  opposite its free end  106 ). The webbing strip  110  extends from the non-free end  112  of the first hook  102  to the non-free end  114  of the second hook  104  (i.e. the end of the hook  104  opposite its free end  108 ) where the strip  110  is threaded through a webbing clamp  116  that is secured to the non-free end  114 . The free end  118  of the webbing strip  110  (i.e. the end of the strip  110  opposite to its end that is attached to the first hook  102 ) hangs freely beyond the clamp  116  to be available for tension to be manually applied as part of the procedure for installing the anchorage  100 , as will subsequently be detailed. 
     The webbing clamp  116  comprises a pivoting snail cam  120  which can pivot around a pivot pin  122  mounted in the body of the clamp  116 . The snail cam  120  is self-tightening under the tension in the strip  110  which normally occurs between the hooks  102  and  104  in use of the anchorage  100 . Such self-tightening of the webbing clamp  116  normally clamps the webbing strip  110  between the cam  120  and the non-free end  114  of the second hook  104  sufficiently tightly as to prevent movement of the strip  110 , and hence to prevent mutual separation of the hooks  102  and  104  during use of the anchorage  100 . When it is desired to release the clamp  116  (e.g. when the anchorage  100  is to be dismounted from the I-beam  10 ), a lever  124  attached to the pivoting cam  120  is manually pushed (in an upwards direction as viewed in FIG. 1) so as to turn the cam  120  around its pivot pin  122  sufficiently clockwise (as viewed in FIG. 1) as to release the webbing scrip  110  from the clamp  116 , whereupon the hooks  102  and  104  can be manually pulled apart to release them from the flange  12 . 
     The first hook  102  is formed with a central aperture  126  in which a first loosely fitting net-hooking sling  128  is fitted such that its free end  130  hangs below the anchorage  100 . Similarly, the second hock  104  is also formed with a central aperture  132  in which a second loosely fitting net-hooking sling  134  is fitted such that its free end  136  hangs below the anchorage  100 . 
     In order to install and use the anchorage  100  (assuming the anchorage  100  initially to be free of the I-beam  100 , and the webbing strip  110  to be threaded through the non-free end  114  of the second hook  104  with a sufficient length between the two hooks  102  and  104 ), the free end  106  of the first hook  102  is hooked around the right flange  14  as shown in FIG. 1, and substantially simultaneously the free end  108  of the second hook  104  is hooked around the left flange  16 . This initial installation step is undertaken such that the hooks  102  and  104  are mutually linked beneath the flange  12  by means of the webbing strip  110  extending between the hooks  102  and  104  as shown in FIG.  1 . Next, the free end  118  of the webbing strip  110  is grasped and pulled to tighten the initially slack webbing strip between the two hooks  102  and  104 , so pulling the hooks  102  and  104  hard against the flanges  14  and  16  respectively. Since the snail cam  120  is self-tightening against movement tending to re-introduce slack into the webbing strip  110  between the hooks  102  and  104 , the webbing clamp  116  will automatically clamp the now slack-free webbing strip  110 , and the hooks  102  and  104  will remain tightly against the flanges  14  and  16  even when this pull on the strip end  118  ceases. When a sufficient number of other anchorages (identical to the anchorage  100  or of a similar design) are installed at distributed locations along the I-beam  10  and/or along adjacent beams, the edges of a safety net (not shown) are hooked over one or both of the free ends  130  and  136  of the net-hooking slings  128  and  134 , and other parts of the safety net edge are similarly hooked onto the other anchorages. 
     In comparison to the prior art practice of winding a rope repeatedly through the net edges and around the beam, the present invention allows safety net anchorages to be simply and rapidly installed while leaving the upper edges of the beams free to support subsequently laid flooring without requiring the safety net to be removed. Since the length of webbing strip  110  extending between the two hooks  102  and  104  can be easily adjusted in a very wide range of lengths (without the use of tools), the anchorage  100  can be readily adjusted to fit I-beams having widths in a correspondingly wide range of widths, and installed on such different flanges without structural modification. 
     When the safety net is no longer required, dismounting of the net and its anchorages is similarly simple and rapid. 
     In suitable circumstances (e.g. if the safety net were provided with its own ties or attachment hooks) the slings  128  and  134  could be omitted, and the safety net directly attached to the hooks  102  and  104 , by way of the apertures  126  and/or  132  or in any other suitable manner. 
     Turning now to FIG. 2, this is an end view of a second embodiment  200  of anchorage in accordance with the invention. The anchorage  200  is generally similar to the first embodiment  100 , but with certain differences in detail. Those parts of the second embodiment  200  that are identical or analogous to equivalent parts in the first embodiment  100  will be given the same reference numerals, but with the leading “1” replaced by a leading “2”, and the following description of the second embodiment  200  will concentrate on the detail differences with respect to the first embodiment  100 . For a description of any part of the second embodiment  200  not given below, reference should be made to the foregoing description of the identical or analogous part in the first embodiment  100 . 
     Apart from the anchorage  200  being laterally transposed on the I-beam  10  in comparison to the positioning on the I-beam of the anchorage  100 , the principal difference in the anchorage  200  with respect to the anchorage  100  lies in the detailed structure and functioning of the clamp  216 . As in the clamp  116 , the lever  224  is pivotable around its pivot pin  222 , but in place of the snail cam  120 , the clamp  216  has pins  221 A and  221 B mounted on the lever  224  parallel to the axis of the pivot pin  222 , at different radial distances from the axis of the pivot pin  222 . Another pin  221 C is fixed on the body of the clamp  216  parallel to the axis of the pivot pin  222 , at the body corner opposite to the corner mounting the pivot pin  222 . (The purpose of the pins  221 A,  221 B, &amp;  221 C will be explained below). 
     A further detail difference in the anchorage  200  with respect to the anchorage  100  lies in the replacement of the net-hooking slings  128  and  134  with respective carabiners  228  and  234  (i.e. strong metal closed-loop shackles with selectively fastenable closures as are commonly employed for securing ends of load-carrying ropes and slings). 
     In order to set up the anchorage  200  for installation, the carabiner  234  is temporarily removed from the body of the clamp  216 , the lever  224  is pivoted fully clockwise (as viewed in FIG.  1 ), the webbing strip  210  is threaded around the pin  221 C, and then looped twice around the pins  221 A and  221 B in the path shown in FIG.  2 . Initially, the webbing strip  210  is slack between the hooks  202  and  204 . The free end  206  of the first hook  202  is hooked around the I-beam flange  16 , and then the free end  208  of the second hook  204  is hooked around the I-beam flange  14 . All slack in the webbing strip  210  is taken up, and then the lever  224  is swung fully anti-clockwise to the position shown in FIG.  2 . This movement of the lever  224  with the webbing strip  210  entrained around the pins  221 A,  221 B, and  221 C tightens the webbing strip  210  between the two hooks  202  and  204 , and forces the hooks  202  and  204  rightly against the flanges  16  and  14  respectively. Finally the carabiner  234  is re-inserted through the aperture  232 , and through a matching aperture in the heel of the lever  224 ; this locks the lever  224  against movement during use of the anchorage  200 , and so prevents inadvertent dismounting of the anchorage  200 . The safety net (not shown) is attached to the appropriate one of the carabiners  228  and  234  according to the principal direction ( 228 N or  234 N) in which the anchorage  200  is stressed in use. 
     As with the first embodiment  100 , since the length of webbing strap  210  extending between the two hooks  202  and  204  in the second embodiment  200  is selectively variable in a very wide range of lengths, the anchorage  200  can be easily adjusted (without the use of tools) to fit I-beams having widths in a correspondingly wide range of widths (such as might be found in the framework of a single building, as well as the width variability that might be expected between different building sites). 
     When the anchorage  200  is no longer required, it is dismounted from the I-beam  10  by reversing the steps of the above-detailed installation procedure. 
     In suitable circumstances (e.g. if the safety net were provided with its own ties or attachment hooks) the carabiners  228  and  234  could be omitted, and the safety net directly attached to the hooks  202  and  204 , by way of the apertures  226  and/or  232  or in any other suitable manner. 
     Turning now to FIGS. 3 and 4, FIG. 3 is an end view of a third embodiment  300  of anchorage in accordance with the invention, and FIG. 4 is a plan view of the third embodiment  300  from beneath (with the I-beam  10  and slings  328 ,  334  omitted for clarity). The anchorage  300  is similar in principle to the first and second embodiments  100  and  200 , but with certain differences in detail. Those parts of the third embodiment  300  that are identical or analogous to equivalent parts in the first and second embodiments  100  and  200  will be given the same reference numerals, but with the leading “1” or “2” replaced by a leading “3”, and the following description of the third embodiment  300  will concentrate on the detail differences with respect to the first and second embodiments  100  and  200 . For a description of any part of the third embodiment  300  not given below, reference should be made to the foregoing description of the identical or analogous part in the first and second embodiments  100  and  200 . 
     In FIG. 3 (as in FIG.  2 ), the anchorage  300  is laterally transposed on the I-beam  10  in comparison to FIG.  1 . The anchorage  300  differs from the first and second embodiments  100  and  200  principally in that the straps  110  &amp;  210  and the clamps  116  &amp;  216  of the adjustable linking means (adjustably linking the first and second hooks) are replaced by a tongue  310  on the non-free end  312  of the first hook  302  interpenetrating a buckle-like non-free end  314  of the second hook  304 . As shown in both FIGS. 3 &amp; 4, the buckle end  314  is provided with longitudinally spaced transverse slots  340  and  342  between which the buckle end  314  is double-cranked to sandwich the tongue  310  an the manner of a buckle sandwiching a belt. A side-tab  344  at the distal end of the tongue  310  prevents the tongue  310  from being pulled free of the slotted buckle end  314 . 
     The near edge of the tongue  310  as viewed in FIG. 3 (the upper edge as viewed in FIG. 4) is formed with a regularly spaced series of rounded notches  346 . In use of the anchorage  300 , the slotted buckle end  314  is latched to the tongue  310  by a latch  316  comprising a longitudinally elongated strip-form detent  348  having a regularly spaced series of projections  350  on the edge of the detent  348  adjacent the tongue notches  346 . The detent  348  is located adjacent one edge of the slotted buckle end  314  (the near edge as viewed in FIG. 3; the upper edge as viewed in FIG.  4 ), longitudinally between the slots  340  &amp;  342 , and sits in the double-cranked portion of the slotted buckle end  314  (which prevents significant longitudinal displacement of the detent  348  with respect to the slotted buckle end  314 ). The detent  348  is laterally movable to a limited extent, and is urged laterally against the notched edge of the tongue  310  by suitable spring means (not shown). Interengagement of the detent projections  350  with the tongue notches  346  latches the buckle end  314  to the tongue  310 , and so inhibits relative movement of the first and second hooks  302  and  304  upon installation of the anchorage  300  (the function of the latch  316  thereby being analogous to the function of the clamps  116  and  216 ). 
     Installation and use of the anchorage  300  is essentially the same as the previously described installation and use of the first and second embodiments  100  and  200  (apart from the use of the latch  316  in place of the clamps  116  and  216 ). In suitable circumstances (e.g. if the safety net to be anchored by the anchorage  300  had its own ties or attachment hooks) the slings  328  and  334  could be omitted and the safety net directly attached to the hooks  302  and  304 , by way of the apertures  326  and/or  332  or in any other suitable manner. The numbers of notches  346  and/or the numbers of projections  350  can be varied from the respective numbers as shown in FIG. 4; in the limiting case, there may be a single projection and/or a single notch (particularly where the anchorage is designed to fit flanges of a uniform width). 
     The anchorages of the invention can be utilised for attaching articles other than safety nets (e.g. for the anchorage of tethered body harnesses for individual fall prevention). 
     While certain modifications and variations of the anchorage in accordance with the invention have been described above, the invention is not restricted thereto, and other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended claims.

Summary:
An anchorage for anchoring an article to a bilateral flange which can have a width in a wide range of widths. First and second hooks are hooked over opposite flanges and securely retained thereon by a webbing strap of adjustable length extending between the two hooks. The webbing strap is permanently secured at one end to one of the hooks, and extends through a clamp on the other hook. The length of the webbing strap between the two hooks is fully adjustable in a wide range to accommodate the varying flange widths. As an alternative to a webbing strap and clamp, the hooks can be adjustably linked by an interpenetrating tongue and slot or buckle, mutually latched at a selected hook separation by a detent having projections urged into notches on the tongue. The anchorage is particularly suitable for securing a safety net to the lower flange of an I-beam in a steel-framed building under construction, since the anchorage is quick and easy both to install and to dismount while easily accommodating a wide range of beam sizes, and always leaves the top edges of beams free to allow them to support flooring without dismounting the anchorage.