Abstract:
A Sheet Metal Structural Member has flanged openings formed therein to permit the passage of services therethrough. A grommet is provided that has a shape that corresponds generally to the plan form shape of the openings. The grommet has a peripheal wall and seating elements arranged about the peripheral wall to mate with the flanges that are located about the flanged opening. The grommet snaps into place and resists movement once installed. The grommet has radiused edges to discourgae damage to service conduits or wiring carried therethrough.

Description:
FIELD OF INVENTION 
     This invention relates to the field of grommets, and, in particular to a grommet that is mountable in a formed aperture in a web section of a formed metal structural member, and a combination of the grommet with a structural member. 
     BACKGROUND ART 
     It is possible to manufacture formed sheet metal posts and beams that can be used as an alternative building material to wooden studs, rafters, stringers, and beams that have been commonly used. It is advantageous to produce such structural members in a manner that may tend to enhance their strength-to-weight ratio, while also tending to reduce the heat loss that may occur across the section of the structural member. As shown in U.S. Pat. No. 5,527,625 of Bodnar, issued Jun. 18, 1996, one way to address these objective is to provide a roll-formed metal member having a web and a pair of opposed flanges, in a generally C-shaped channel-like section, and then to blank the web to leave alternating diagonal struts with formed flanges such that the remaining web has a somewhat truss-like appearance when viewed perpendicular to the web. 
     The manner in which the openings are formed through the web of the structural member, and the manner of forming the flanges, is such that it is advantageous to provide a relatively smoothly radiused transition into the web adjacent to the opposed out-of-plane flanges. 
     In a conventional wooden stud or rafter, services, such as electrical power wiring, plumbing, telephone or other communications wiring, or built-in vacuum lines, may tend to be carried though holes bored in the mid-section of the stud or rafter. Wooden studs tend not to be good electrical conductors, and may tend to dampen vibration. In most cases services can be mounted directly in contact with the wood. It is not desirable to have holes bored in sheet metal structural members on the job site, since this is a process over which there is very little quality control, and hence significant opportunity to impair the structural performance of the section. Furthermore, in a formed sheet metal structural member that has had openings blanked in it, and flanged struts formed in it adjacent to the openings, there may be little or no need to drill additional openings. 
     However, while it would be possible to run services directly through the openings formed in the web, it may also be undesirable. The formed metal member may have sharp edges, and it may tend not to be practical to have all of those edges smoothed down. It may not be desirable to have electrical wiring chafe against a sharp metal edge over a period of time, under vibration loads. Similarly, it may not be desirable to run water pipes, whether hot or cold, in direct contact with the metal section. For these reasons an intermediate isolating or cushioning member may be desired. 
     A cushioning member, or grommet, for use with the formed sheet metal structural member has a number of desirable properties. In a construction project such a grommet may be required at one or more formed openings in every stud in a wall, and in one or more walls in every room in a house or other building. The person installing the grommets may do so many times per day. An installation that requires complicated tools or procedures is unlikely to be one that will be undertaken with a high level of diligence on a repetitive basis, particularly as the installer grows weary or disinterested. 
     While it is advantageous for the grommet to be easily installed, it is also desirable that the grommet not tend to be too easily removed. The grommet may be required to stay in service for many years. A loose fit may not be desirable, particularly if vibration is a concern, as it may be in a water pipe fitting, or a fitting subject to repetitive loading over a relatively long period of time. 
     In the type of sheet metal structural member in question, the depth of the strut flanges may tend to be greatest at mid strut, and may tend to be reduced in the radiused corners where the struts meld into the margin of the web that adjoins the flanges. The dimensional control over the distance from strut to strut may tend to be poorest at mid strut, and relatively greater in the corners of the opening adjacent to the web margin. The web margin may also tend to be a region of lesser potential for deflection due to vibration than the mid strut region. It is advantageous to have an insulating grommet that is capable of engaging the root corners of the formed opening. 
     It is advantageous to produce a family of grommets of the same, or similar, base width dimension, each having a different attitude for use with a different width of structural member, rather than using the same longitudinal base to cross-web altitude aspect ratio. The use of the same aspect ratio grommet at different sizes would correspond to structural members having greater pitch centers between adjacent openings. When using a rotary press with interchangeable dies, the pitch center distance is determined by the fixed radius of the successive pivot axes of the rotary dies carriers and seats. Since it is difficult to change this dimension it is advantageous to change the height of the openings transverse to the web, while maintaining the pitch between openings at a constant distance. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention there is a grommet, for use with a structural member having a web and an opening defined in the web. The opening has flangework adjacent the opening. The grommet is insertable into the opening when moved forwardly along an insertion direction. The grommet comprises a peripheral wall defining a passageway therewithin. The wall has a leading portion for insertion into the opening and a trailing portion; and at least two seating elements extending outwardly from the trailing portion of the wall to prevent the trailing portion from passing through the opening. The grommet has at least two abutments connected to the peripheral wall. The abutments are moveable to a deflected position to permit entry of the leading portion into the opening, and the abutments are biased outwardly relative to the peripheral wall to an opposed position relative to the seating elements. The seating elements are spaced from the abutments in the insertion direction to permit the web flangework to be captured therebetween. The abutments and the seating elements are spaced about the peripheral wall to inhibit forward and rearward motion of the grommet relative to the structural member in the insertion direction when the abutments are in the opposed position. 
     In an additional feature of that aspect of the invention, at least one of the seating elements is resilient. The grommet is moveable to an inserted position relative to the structural member. In the inserted position the abutments are able to move to the opposed position and the resilient seating element is pre-loaded. The pre-loaded resilient seating element is operable to exert a rearward force on the abutments. 
     In another additional feature of that aspect of the invention, at least one of the seating elements is resilient and has a distal tip region that is cantilevered outwardly from the peripheral wall. The distal tip region has a forwardly protruding formation thereon. The grommet is moveable to an inserted position relative to the structural member. In the inserted position the abutments are able to move to the opposed position and the forwardly protruding formation is engageable with the structural member to cause the distal tip region to deflect rearwardly relative to the peripheral wall, thereby applying a pre-load to the resilient seating element. The pre-loaded resilient seating element is operable to exert a rearward force on the abutments, thereby squeezing the structural member between the abutments and the seating elements. 
     In a further additional feature of that aspect of the invention, the seating elements include flanges cantilevered out from the peripheral wall. The flanges have a rearward face and a distal edge, and, when installed on the structural member, the rearward face of the cantilevered flange adjacent to the distal edge stands rearwardly relative to the remainder of the cantilevered flange. 
     In a still further additional feature of that aspect of the invention, the grommet has a divider extending internally of the peripheral wall to define a second passage therewithin. 
     In yet a further additional feature of that aspect of the invention, the divider is placed to lie outside the largest inscribed circle that can be constructed within the peripheral wall. 
     In yet still a further additional feature of that aspect of the invention, the trailing portion of the peripheral wall has an outwardly extending flange mounted thereon. The flange is substantially planar. 
     In another aspect of the invention, there is a grommet, for use with a structural member having a web and an opening defined in the web. The opening has at least three smoothly radiused corners and a flanged lip adjacent thereto. The grommet is moveable in a forward direction for insertion into the opening. The grommet comprises a peripheral wall having corner portions and side portions extending between the corner portions. The grommet has at least one passageway defined therethrough within the peripheral wall. Attachment fittings extend outwardly from at least three of the corner portions. Each of the fittings has a seating element extending outwardly relative to the wall and an abutment element mounted forwardly of the seating element. Each of the seating elements is engageable to one of (a) the web, and (b) the flanged lip adjacent to a corner of the opening. Each of the abutment elements is engageable to the other of (a) the web, and (b) the lip. The abutment element is moveable to a deflected position to permit introduction of the grommet into the opening, and biased to move to an opposed position relative to its corresponding seating element. The abutment and the seating element is co-operable to capture the web and the lip therebetween. When so captured, the abutment element in the opposed position is biased to discourage disengagement of the grommet from the opening. 
     In an additional feature of that aspect of the invention, the side portions are substantially straight and each has an inside face. The grommet has at least one partition wall lying inwardly of the peripheral wall to define at least one other passageway through the grommet. 
     In another additional feature of that aspect of the invention, the partition wall lies outside the largest inscribed circle that can be constructed inside the peripheral wall. 
     In a further additional feature of that aspect of the invention, the grommet has a plurality of partition walls. The partition walls co-operate with the peripheral wall to define a plurality of passageways through the grommet. 
     In a still further additional feature of that aspect of the invention, the side portions have respective leading portions and trailing portions. The seating elements extend outwardly from the corner portions adjacent the respective trailing portions and the abutment elements have a cam face oriented outwardly from the corner portions adjacent the respective leading portions. 
     In yet a further additional feature of that aspect of the invention, the corner portions comprise an archway having a pair of side columns and a spanning member. The abutment element depends from the spanning member. 
     In yet still a further additional feature of that aspect of the invention, the side portions extend linearly between the corner portions. The corner portions have corner wall facings standing outwardly of the walls such that a straight edge laid across the corner wall facings stands clear of the side wall lying therebetween. 
     In another additional feature of that aspect of the invention, at least one of the seating elements includes an outwardly cantilevered resilient member. 
     In yet another additional feature of that aspect of the invention, the sidewalls have a trailing edge, and the trailing edge has an outwardly extending flange formed thereon. 
     In yet still another additional feature of that aspect of the invention, at least one of the seating elements is resilient. The grommet is moveable to an inserted position relative to the structural member. In the inserted position the abutments are able to move to the opposed position and the resilient seating element is pre-loaded. The pre-loaded resilient seating element is operable to exert a rearward force on the abutments. 
     In a further additional feature of that aspect of the invention, at least one of the seating elements is resilient and has a distal tip region that is cantilevered outwardly from the peripheral wall. The distal tip region has a forwardly protruding formation thereon. The grommet is moveable to an inserted position relative to the structural member. In the inserted position the abutments are able to move to the opposed position and the forwardly protruding formation engages the structural member to cause the distal tip region to deflect rearwardly relative to the peripheral wall, thereby applying a pre-load to the resilient seating element. The pre-loaded resilient seating element is operable to exert a rearward force on the abutments, thereby squeezing the structural member between the abutments and the seating elements. 
     In yet a further additional feature of that aspect of the invention, the seating elements include flanges cantilevered out from the peripheral wall. The flanges have a rearward face and a distal edge, and, when installed on the structural member, the rearward face of the cantilevered flange adjacent to the distal edge stands rearwardly relative to the remainder of the cantilevered flange. 
     In still yet a further additional feature of that aspect of the invention, the peripheral wall has three planar side portions and three corner fitments. An outwardly extending flange surmounts the trailing edge of each of the side portions, the trailing face of the flanges being co-planar. The corner portions each include an archway having columns and an overspanning member. Each of the columns mate with an end of an adjoining side portion and the inner face of the arch has a skirt mounted thereacross. A resilient catch member is mounted to depend from the arch. The abutment is a rearwardly facing surface of the catch member. The catch member has an outwardly and rearwardly tapering cam surface. The cam surface is moveable to deflect the abutment inwardly. The columns are mounted to stand outwardly of the side wall portions to define a clearance rebate therebetween. The seating element includes a cantilevered flange extending outwardly about the corner portion and mating with the outward flanges of the trailing portions of the side wall portions. The cantilevered flange is resilient. 
     In another aspect of the invention, there is the combination of at least one beamlike longitudinally extending structural member, and at least one grommet for use in cooperation therewith. The structural member has a web. The web has a longitudinal edge, and a longitudinally extending main flange running along the edge. The web has at least one opening therein, and flangework formed adjacent to the opening. The grommet has a peripheral wall having an internal face defining a passageway. The wall has a leading portion that can be introduced into the opening in the web, and a trailing portion having at least one seating element extending outwardly of the wall to prevent passage of the trailing portion fully through the opening. The grommet has at least one biased member having an abutment element biased to an opposed position relative to the seating element. The biased member is moveable to a deflected position during introduction of the trailing portion into the opening. The grommet is moveable to engage the seating element against one of (a) the flangework and (b) the web, and, when so engaged the abutment element is moveable to the opposed position under the influence of the biased member. In the opposed position the abutment element discourages removal of the grommet from the opening. 
     In still another additional feature of that aspect of the invention, the opening has a periphery defined in the web. The peripheral wall has at least one side wall portion extending between a pair of sidewall ends. One of the seating elements and one of the abutment elements are located at each end thereof, and, in an installed position of the grommet relative to the structural member the side wall portion has a span free of contact with the periphery of the opening. 
     In yet another additional feature of that aspect of the invention, the structural member has a pair of opposed main flanges extending along opposite edges of the web. A plurality of the openings are formed in the web. Each of the openings has a base side portion extending parallel to one of the main flanges and a pair of side portions extending from the base side to meet at a smoothly radiused apex opposite the base side portion. The openings are arranged along the web in alternating side-by-side fashion with alternating diagonally extending struts formed in the web between pair of adjacent openings. The flangework extends along the struts and the base side portions. 
     In still yet another additional feature of that aspect of the invention, the opening has a base side portion extending parallel to the main flange and a pair of side portions extending from the base side to meet at a smoothly radiused apex opposite the base side portion. The side portions and the base portion of the opening meet at smoothly radiused base corners. The grommet engages the flangework at the base corners and at the apex. 
     In another additional feature of that aspect of the invention, the grommet has a base portion locatable adjacent the base portion of the opening, and a pair of side portions locatable adjacent to the side portions of the opening. The base portion and the side portions of the grommet meet at respective attachment fittings that seat in the corners and the apex of the opening. 
     In still yet another additional feature of that aspect of the invention, the flangework forms a continuous peripheral lip around the opening. 
     In a further additional feature of that aspect of the invention, the apex has a larger radius of curvature than either of the base corners. 
     In yet a further additional feature of that aspect of the invention, the web lies in a web plane. Portions of the flangework extend about the corners and the apex of the openings. The portions of the flangework have respective distal edges formed out of the plane of the web at a tapered angle whereby the entrance of the opening at the plane of the web is wider than the exit of the opening adjacent the distal edges. The leading portion is moveable along an insertion direction running from the entrance toward the exit of the opening. 
     In still yet a further additional feature of that aspect of the invention, the attachment fittings have column members shaped to conform to the taper of the flangework at the corners and at the apex. 
     In another additional feature of that aspect of the invention, each attachment fitting includes one of the abutments, one of the seating elements, and has a pair of the column members and an overspanning member attached thereto adjacent the leading portion of the grommet. Each attachment fitting has an arm depending from the overspanning member. The arm has the abutment formed thereon, and has an outwardly facing cam member engageable with the taper of the flangework to cause the abutment to deflect. In the opposed position the abutment engages the distal edge of the flangework. 
     In yet another additional feature of that aspect of the invention, each of the seating elements has an outwardly extending resilient wing. The resilient wing waves an interface member for engaging the web. The resilient member is operable to exert a rearward force on the abutment when the grommet is engaged with the structural element. 
     In a further additional feature of that aspect of the invention, the grommet includes at least one internal partition to define a plurality of passageways therethrough. 
     In a still further aspect of the invention, there is a kit comprising at least one sheet metal structural member and at least one grommet for use in co-operation therewith. The sheet metal structural member has a pair of opposed, spaced apart, parallel main flanges and a web extending therebetween. The web has an outer face lying predominantly in a web plane and an inner face lying to one side thereof The main flanges extend perpendicularly to the web plane and away from the outer face, to give the sheet metal structural member a C-shaped appearance when viewed from one end thereof The web has a plurality of triangular openings formed therein in an alternating arrangement, and a plurality of alternating, flanged diagonal struts formed between adjacent pairs of the openings. The openings have smoothly radiused corners. The web has lip flangework formed therein adjacent each opening. The lip flangework stands proud of the inside face of the web. The grommet has a peripheral wall having an internal face defining a passageway. The wall has a leading portion that can be introduced into one of the openings in the web, and a trailing portion having at least one seating element extending outwardly of the wall to prevent passage of the trailing portion fully through the one opening. The grommet has at least one biased member having an abutment surface biased to an opposed position relative to the seating element. The biased element is moveable to a deflected position during introduction of the trailing portion into the one opening. The abutment element and the seating element defines a capture depth at least great enough to capture the lip flangework and the outer face therebetween when the seating element engages the sheet metal structural member and the abutment surface moves to the opposed position. 
     In an additional feature of that aspect of the invention, the lip flangework is continuous flange extending about the triangular opening. 
     In a further additional feature of that aspect of the invention, the smoothly radiused corners of adjacent openings define root portions of the struts adjacent the corners. The grommet has three seating elements and three biased members, spaced about the peripheral wall in positions to engage the sheet metal structural member adjacent the smoothly radiused corners of the opening. 
     In yet a further additional feature of that aspect of the invention, portions of the flangework extend about the corners and apex of the opening. The portions of the flangework have respective distal edges formed out of the web plane at a tapered angle such that the entrance of the opening at the plane of the web is wider than the exit of the opening adjacent the distal edges. The leading portion is moveable along an insertion direction running from the entrance toward the exit of the opening. The grommet has attachment fittings locatable in the corners and the apex of the opening. The attachment fittings have column members shaped to conform to the taper of the flangework at the corners and at the apex. 
     In still yet a further additional feature of that aspect of the invention, portions of the flangework extend about the corners and the apex of the opening. The portions of the flangework have respective distal edges formed out of the web plane at a tapered angle such that the entrance of the opening at the web plane is wider than the exit of the opening adjacent the distal edges. The grommet includes attachment fittings engageable with the structural member adjacent the corners and apex of the opening. Each of the attachment fittings includes one of the abutments, one of the seating elements, has a pair of the column members and an overspanning member attached thereto adjacent the leading portion of the grommet. Each attachment fitting has an arm depending from the overspanning member. The arm has the abutment formed thereon, and has an outwardly facing cam member engageable with the taper of the flangework to cause the abutment to deflect. In the opposed position the abutment engages the distal edge of the flangework. 
     In yet another additional feature of that aspect of the invention, each of the seating elements has an outwardly extending resilient wing. The resilient wing waves an interface member for engaging the web, and the resilient member is operable to exert a rearward force on the abutment when the grommet is engaged with the structural element. 
     In a further additional feature of that aspect of the invention, the peripheral wall has corner portions and straight side portions extending between the corner portions. The corner portions have corner wall facings standing outwardly of the walls such that a straight edge laid across the corner wall facings stands clear of the side wall lying therebetween. 
     In yet a further additional feature of that aspect of the invention, the grommet has at least one partition wall lying inwardly of the peripheral wall to define at least one other passageway through the grommet. 
     In another aspect of the invention, there is the combination of at least one beam-like structural member that extends in a longitudinal direction, and at least one grommet for use in co-operation therewith. The structural member has a planar web. The web has a straight longitudinal edge, and a longitudinally extending main flange running along the edge. The web has a plurality of alternating wide portions and narrow portions defining a longitudinal zig-zag edge. The web has an opening defined in each of the wide portions. Each opening has a base portion parallel to the edge and a pair of side portions extending away from the base portion to meet at an apex. The opening has smoothly radiused corners between the base portion and the side portions, and at the apex. The structural member has a lip flange formed about the opening. The lip flange has a distal edge lying away from the web. The grommet has a peripheral wall having an internal face defining a passageway. The wall has a leading portion that can be introduced into the opening in the web, and a trailing portion having at least one seating element extending outwardly of the wall and engageable with the web to prevent passage of the trailing portion fully through the opening. The grommet has at least one biased member having an abutment element biased to an opposed position relative to the seating element. The biased member is moveable to a deflected position during introduction of the trailing portion into the opening. The grommet is moveable to engage the seating element with the web and the abutment element with the lip flange to capture the web. In the opposed position the abutment element discourages removal of the grommet from the opening. 
     In an additional feature of that aspect of the invention, the opening has a generally isosceles triangular shape, dividing the wide portion into a pair of strut-like portions. The peripheral wall has three straight side portions and three corner fittings. One of the corner fittings is sized to fit the apex, and the other two of the fittings is sized to fit the other two corners of the opening. The corner fittings stand proud of the side portions such that a straight edge placed across any two of the fittings stands clear of the straight side portion lying therebetween. 
     In a further additional feature of that aspect of the invention, the fittings each include one of the abutment and one of the seating elements, and the fittings act against the web and the lip flange at the corners of the opening. 
     In yet a further additional feature of that aspect of the invention, an outwardly extending flange surmounts the trailing edge of each of the side portions. The trailing face of the flanges is co-planar. The seating element includes a cantilevered flange extending outwardly about the corner portion and mating with the outward flanges of the trailing portions of the side wall portions. The cantilevered flange is resilient and has a portion engageable with the web. The corner portions each include an archway having columns and an overspanning member. Each of the columns mates with an end of an adjoining side portion and the inner face of the arch has a skirt mounted thereacross. A resilient catch member is mounted to depend from the arch. The abutment is a rearwardly facing surface of the catch member. The catch member has an outwardly and rearwardly tapering cam surface. The cam surface is moveable to deflect the abutment inwardly. The grommet is movable to a seated position relative to the structural member, and, in the seated position, the resilient member bears against the web under a pre-load and carries and exerts a force to urge the abutment to bear against the distal edge of the lip flange. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a general arrangement, perspective view of a pair of sheet metal structural members of different sizes each grommets mounted therein according to the principles of the present invention; with additional small and large grommets shown in the foreground; 
     FIG. 1 b  is a cross-sectional view of a strut of one of the structural members of FIG. 1 a  taken on section ‘ 1   b - 1   b’,    
     FIG. 1 c  is a partial cross-sectional view of a corner portion of one of the structural members of FIG. 1 taken on ‘ 1   c - 1   c’;    
     FIG. 2 a  is an isometric view of the large grommet of FIG. 1; 
     FIG. 2 b  is a plan view of the grommet of FIG. 2 a;    
     FIG. 2 c  is a plan view of the grommet of FIG. 2 a  taken opposite to FIG. 2 b;    
     FIG. 2 d  is a detail view of the grommet of FIG. 2 a  taken on arrow ‘ 2   d’;    
     FIG. 3 a  is a side view, in section, of the grommet of FIG. 2 a  as it is about to enter an opening in a structural member; 
     FIG. 3 b  is a side view, in section, of the grommet of FIG. 2 a  as it is being introduced into the opening of FIG. 3 a;    
     FIG. 3 c  is a side view, in section, of the grommet of FIG. 2 a  in a seated position relative to the structural member of FIG. 3 a;    
     FIG. 4 a  shows a plan view similar to FIG. 2 b  of an alternate embodiment of grommet having internal partitions; 
     FIG. 4 b  shows a further alternative embodiment to the grommet of FIG. 2 b;    
     FIG. 4 c  shows another alternative embodiment to the grommet of FIG. 2 b.    
     FIG. 4 d  shows yet another alternative embodiment to the grommet of FIG. 2 b;    
     FIG. 5 a  shows a top plan view of the small grommet of FIG. 1 a;    
     FIG. 5 b  shows a bottom plan view of the grommet of FIG. 5 a;    
     FIG. 5 c  shows a cross-section of the grommet of FIG. 5 a  on section ‘ 5   c - 5   c’;    
     FIG. 6 a  shows a side view of an alternate embodiment of structural member to the structural member of FIG. 1; 
     FIG. 6 b  shows a cross-sectional view of the structural member of FIG. 6 a;    
     FIG. 7 a  shows a side view of another alternate embodiment of structural member to the structural member of FIG. 1; 
     FIG. 7 b  shows a sectional view of the structural member of FIG. 7 a;    
     FIG. 8 a  shows a side view of another alternate embodiment of structural member to the structural member of FIG. 1; 
     FIG. 8 b  shows a sectional view of the structural member of FIG. 8 a;    
     FIG. 9 a  shows an alternate cross-section to the cross section of FIG. 3 a;    
     FIG. 9 b  shows another alternate cross-section to the cross-section of FIG. 3 a;    
     FIG. 9 c  shows a further alternate cross-section to the cross-section of FIG. 3 a;    
     FIG. 10 a  shows a side view of another alternate embodiment of structural member to the structural member of FIG. 1; 
     FIG. 10 b  shows an isometric view of a pair of structural members as in FIG. 10 a  with tips embedded in concrete; 
     FIG. 10 c  is a detail of a flanged opening and embedment formation of the structural ember of FIG. 10 a;    
     FIG. 11 a  shows an alternate cross-section for the structural member of FIG. 10 a;    
     FIG. 11 b  shows another alternate cross-section for the member of FIG. 10 a;    
     FIG. 11 c  shows a further alternate cross-section for the member of FIG. 10 a;    
     FIG. 12 a  shows a side view of a pair of structural elements joined together; and 
     FIG. 12 b  shows a cross-sectional view of the elements of FIG. 12 a.   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description which follows, and the embodiments described therein, are provided by way of illustration of an example, or examples of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features of the invention. 
     Referring to FIGS. 1 a ,  3   a ,  3   b , and  3   c , a sheet metal structural member is indicated generally as  20 . It has a web  22  and a pair of generally opposed, longitudinally extending parallel main flanges  24  and  26  that extend perpendicularly out of the plane of web  22  to form a generally ‘C’ shaped channel section, with the toes of flanges  24  and  26  having an inwardly bent lip  28 ,  30 . In the example of FIG. 1, member  20  has width and depth dimensions to simulate a (nominal) 2″×6″, although 2″×4″ studs (seen in the background of FIG.  1  and indicated as  32 ), 2″×8″ beams or other stud or beam sizes can also be formed. Web  22  can be termed the back of the C-channel section, and lies, generally, with its outer face  34  in a web plane indicated as ‘W’. The inner face  36  of web  22  lies to one side of web plane ‘W’, and the legs of the section, main flanges  24  and  26 , extend to the same side of plane ‘W’. The longitudinal direction is indicated by an ‘X’, the axial direction perpendicular to ‘X’ and lying in plane ‘W’ is indicated as ‘Y’ and the axial direction perpendicular to plane ‘W’ is indicated as ‘Z’. The width of web  22 , and the overall depth of structural member  20 , are measured in the ‘Y’ direction, and the width of main flanges  24  and  26  is measured in the ‘Z’ direction. 
     Web  22  of member  20  has been blanked and formed to leave an array  38  of alternating diagonal struts  40  and  42  that extend between web margins  44  and  46  whence flanges  24  and  26  extend. Openings, of which one representative example is indicated as  48 , are defined in the spaces bounded by respective diagonal struts  40  and  42 , and margins  44  and  46 , as the case may be. 
     A one-piece, snap fit grommet  60  is mounted to member  20  by being pushed into opening  52  in the insertion direction indicated by arrow ‘P’. Opening  52  is, for the purposes of this description, identical to any one of openings  48 ,  50  or  54 , such that grommet  60  could be mounted in any of them, interchangeably. Grommet  60  provides a protected port for services, such as a water pipe or electrical conduit or cable (not shown) to traverse web  22 . 
     Opening  48 , being typical, will now be described in detail. It has a generally triangular shape, having a first radiused corner defined at the altitudinal vertex, or apex  62 , lying between struts  40  and  42 , a second, radiused base corner  64  lying between strut  40  and margin  44 , and a third, radiused corner  66  lying between strut  42  and margin  44 . In general, the triangular shape so defined is an isosceles triangle. The radius at base corners  64  and  66  is smaller than the larger, more generous radius of apex  62 . As shown, the base  68  of the triangular shape lies along margin  44 . Bases  67  and  69  of the adjacent triangular openings, indicated as  50  and  54 , lie along the margin  46 , each triangle alternating in orientation relative to its neighbours. 
     Flangework, in the nature of a continuous rim, or lip flange  70  is formed out of the plane of web plane ‘W’ in the direction away from outer face  34 , and extends fully about the periphery of opening  48 . Lip flange  70  includes left and right hand strut flanges  72 ,  74  that extend along the sides of struts  40 ,  42  and a base side flange  76  formed on margin  44  (similar flanges extend along the sides of the adjacent opening,  50 ). In each of base corners  64  and  66  there is a corner flange portion  80 ,  82  whose free edge  84 ,  86  lies at a shallower depth than the free edge of flanges  72  or  74 , and at a shallower depth than the free edge of the medial portion  88  of flange  76 . Lip flange  70  also includes an apex flange  87  which runs along apex  62  and smoothly into strut flanges  72  and  74 . 
     Each of struts  40  and  42  has a medial portion  90  and root portions  92 ,  94  at either end. In each of root portions  92 ,  94  there is a generally triangular indentation  96 ,  98  stepped to one side of plane ‘W’ of web  22  generally. Each of indentations  96 ,  98  has a generally straight base side  100 , another side  102  facing the altitudinal vertex of the adjacent opening, and a curved side  104  sharing a center of curvature with base corner  64  or  66  as the case may be. In section, medial portion  90  has a back  106  lying in the plane of web  22  generally, and a pair of formed legs, being flanges  72  and  73  in the case of strut  40 , and flanges  74  and  75  in the case of strut  42 . 
     Flanges  72  and  73  (and  74  and  75 ) lie at an out-of-plane true angle to the plane of web  22  generally that is indicated by a such that flanges  72  and  73  present a tapered wall that has a root at back  106  and a distal edge lying away from web ‘W’. By comparison, corner flange portion  80  (and  82 ) is formed on an angle β to extend away from plane ‘W’ and presents a tapering surface with a distal edge  84 , β being less than α. 
     Grommet  60  also is shaped to conform, generally, to the shape of opening  48  (or  50 ,  52 ,  54  as shown). Grommet  60  has a peripheral wall  110  having a base side  112 , base corners  114  and  116 , a pair of sides  118  and  120  rising toward an altitudinal corner, or apex  122 . As such, it has a general shape in plan view of an isosceles triangle, with truncated corners. Attachment fittings  124 ,  126  and  128  are located at respective corners  114 ,  116  and apex  116 . Peripheral wall  110  has a forward or leading portion,  130 , that is, the portion that is first introduced into opening  48  during insertion of grommet  60 , and a rearward or trailing portion  132  that follows the leading portion during insertion. 
     Each of sides  112 ,  118  and  120  has a cross-section as shown in FIG. 3 a . Each has a side wall or leg,  134  that is generally rectangular in section, and a trailing edge flange  135  extending perpendicularly relative to leg  134 . Leg  134  is slightly tapered, having a draft angle to facilitate removal from the mold on manufacture. Leg  134  has an inner face  136  that faces inwardly toward, and defines a portion of the boundary of, an internal passageway  140 . Internal passage  140  extends generally in the direction of insertion indicated by arrow ‘A’, and is formed to carry services through web  22 , such as plumbing, wiring, vacuum hoses, or other hardware. Leg  134  also has an external, or outer face  138  that faces outward relative to passageway  140 . 
     Corners  114  and  116  are right and left hand images of each other. If sides  112 ,  118 , and  120  were extended they would meet at a sharp corner. Instead they are truncated at the respective corner sub A. At the points where sides  112 ,  118  and  120  are truncated in this way, grommet  60  has corner webs  142 ,  143 , and  144  which form part of, and complete, the boundary of passageway  140  formed by peripheral wall  110 . 
     For the purposes of description, attachment fitting  128  at apex  122  differs from attachment fittings  124  and  126  only in size, corner radius, aspect ratio and other dimensions rather than in nature. Thus, although only one fitting is described, the description is applicable to the fittings as well. 
     Each attachment fitting has an archway  146  having a pair of left and right hand columns  147  and  148  surmounted by an overspanning member in the nature of a lintel  150  that surmounts the distal ends of columns  147  and  148  and has a forward surface lying flush with the leading edge  152  of peripheral wall  110 . Columns  147  and  148  stand outwardly from peripheral wall  110 . That is, the inner edge of columns  147  and  148  back on the adjacent sidewall portions while their outer left and right hand edge facings  153  and  154  stand outwardly of the planes defined by outer faces  138  of the respective wall portions. In side view, as seen in the detail of FIG. 2 d , the leading portion of column . 147  (and  148 ) has a rake angle ψ such that column  147  (or  148 ) is wider at its base than at its distal end. A straight edge placed across a pair of columns at either end of any of side portions  112 ,  118  or  120  will stand clear of their respective outer faces,  138 . That is, a rebate  156  formed between outer surface  138  and the columns at either end thereof 
     Further, facings  153  and  154 , and the outward edge of lintel  150  are formed to conform to an arcuate surface, such that the leading end of grommet  60  can be introduced into opening  52 , and so that facings  153  and  154  seat in the smoothly curved corners of, for example, opening  48 ,  50 ,  52  or  54 . 
     Each attachment fitting  124 ,  126 , or  128  includes a catch member  160  that depends from lintel  150 . It has an outwardly oriented tapered facing, in the nature of a fluted cam face  162 , the taper being such that the depending edge  164  is biased to stand further outwardly than facings  153  and  154 . A shoulder, in the nature of a rearwardly facing abutment  166  extends inwardly from edge  164  to terminate at a rearwardly extending depending skirt, or tab  168  of catch member  160 . In operation, when grommet  60  is moved forward along the insertion direction, cam face  162  will tend to engage the arcuate tapering surface of one or another of corner flange portions  80 ,  82  and apex flange  87 . This will in turn tend to cause catch member  160 , and hence abutment  166  to deflect inwardly into the alcove, or chamber, defined inside archway  146 . Catch member  160  is resilient, and is biased outwardly. When grommet  60  is advanced sufficiently far for edge  164  to clear the distal edge  169  of the respective corner flangework, abutment  166  is able, under the bias of catch member  160 , to move outwardly to engage distal edge  169 . In this outward position abutment  166  discourages rearward movement of grommet  60 , preventing its removal from opening  52 . 
     Each attachment fitting  124 ,  126  or  128  also includes a seating element  170  in the nature of an outwardly extending cantilevered wing  172  that has a pair of left and right hand flange extensions  174  and  176  that lie flush with, and are smoothly rooted into flanges  135 , of peripheral wall  110 . An arcuate bridging member  178  lies in the same plane as, and connects the distal ends of, flange extensions  174  and  176 . As thus arranged the trailing edge of web  142 ,  143 , or  144  as the case may be, the inside edge of flange extensions  174  and  176 , and the inside edge of bridging member  178  define a port  179  through which mold extensions may move during fabrication of grommet  60  to form the underside of lintel  150  and the inward or rearward face of catch member  160 . 
     On the leading face of each seating element is a forwardly protruding nub  180  that engages the outer face  34  of web  22  when grommet  60  is inserted. Seating element  170  is resilient. When the trailing face of grommet  60  is pushed forward enough to cause abutment  166  to snap into position, the forward motion also causes nub  180  to seat against web  22 , and, in so doing, a pre-load is applied to seating element  170 . In this position abutment  166  sits in a position that is generally opposed to seating element  170  and the space between them, measured in the direction of insertion, is sufficient to permit capture of apex flange  87  (or flange portions  80  or  82  as the case may be) and web  22 . When grommet  60  is left in place, the preload in seating element  170  will tend to bias peripheral wall  110  rearward relative to the insertion direction, and in so doing, will tend to exert a force to urge abutment  166  more firmly against distal edge  169 , thus tending to immobilise grommet  60 . This preload may also tend to help grommet  60  resist loosening and rattling under modest vibration. 
     When grommet  60  is seated in this way in opening  48 ,  50 ,  52  or  54 , the outer faces  138  of leg  134  of each of the three sides of peripheral wall  110  will stand clear of the corresponding facing portions of flangework lip flange  70 . This increases the likelihood that vibration loads will not be transferred to or from the mid sections of the struts, but rather will be carried to the corners at margins  44  and  46 . 
     In alternative embodiments, other geometric arrangements of seating element can be used. For example, flange extensions  174  and  176  could be curled forward to present a leaf-spring-like arrangement for deflection on insertion. Not all of the seating elements need be resilient. In some cases it may not be desirable to have any pre-loaded seating elements, in others a single pre-loaded element or spring would suffice to pre-load all of the fittings. For example, although the configuration shown in FIGS. 2 a ,  2   b  and  2   c  is preferred, a grommet having a pair of abutments (or seating elements) located at the mid-portion of the long sides  118  and  120  could be opposed by a pair (or more) of seating elements (or, abutments) arranged in the corners, or one at apex  122  and one along the middle of the base side  112 . A single spring loaded element, among a total of four seating elements and abutments, would then serve to pre-load all of the others. 
     In an alternative embodiment as shown in FIG. 4 a , a grommet  181  has three internal dividers  182 ,  184 , and  186  that subdivide the space enclosed within a peripheral wall  188 , similar in other respects to peripheral wall  110  described above. An allowable maximum outer pipe diameter φ is defined by the largest circular section that can be inscribed within side wall portions  192 ,  194  and  196 , and is shown in dashed lines in main passageway  198 . (It will be appreciated that a slightly larger pipe can be carried, or the enclosure of peripheral wall  188  can be made slightly smaller, if an interference fit is desired.) As illustrated, each of dividers  182 ,  184  and  186  is located outside the circle of diameter φ, and the subsidiary passages so formed, indicated as  200 ,  202  and  204 , are available to carry other services. Dividers  182 ,  184 , and  186  need not be straight walls, or webs, but could be formed on a circular arc, as shown at  206  in FIG. 4 b . Alternatively, as shown in FIG. 4 c  a spider  208  having a circular center  210 , such as may be suited to a water pipe, and outwardly radiating partitions in the nature of dividers  212  could be used. One or two dividers could be used rather than three as shown, or more dividers could be used depending on the number, shape and size of the passageways to be formed. In FIG. 4 d  a single divider  214  divides the internal passageway into a minor section  216  for a pipe  217  (shown in dashed lines) and a major portion  218  for other services. Divider  214  is bent so that the long sidewalls of the grommet can be squeezed inward to flex divider  218 , and, when released it holds snug against pipe  217 . 
     Grommet  60  is a molded part made from a polypropylene homopolymer plastic. It is considered to be and may tend to function as an electrical insulator. The edges of grommet  60  that face inward toward passageway  140 , or that stand rearwardly of web  22  when installed, have a small radius (typically 0.047″) to decrease the likelihood that service conduits or cables passing through grommet  60  will encounter a sharp edge. In the specific embodiment illustrated in FIG. 2 a , grommet  60  is of a size to fit an opening in a (nominal) 2×6 member. 
     Alternative sizes of grommet can also be made, as typified by grommet  220  shown in the foreground of FIG. 1 a , and installed in the (nominal) 2″×4″ structural member  38  lying in the background of FIG. 1 a . Grommet  220  is shown in top, bottom and sectional views in FIGS. 5 a ,  5   b  and  5   c  respectively. It has attachment fittings  222 ,  224 , and  226  of the same nature and features as attachment fittings  124 ,  126  and  128 . Openings  230 ,  232 , and  234  defined in web  236  of structural member  38  have the same pitch between centers as openings  48 ,  50 ,  52  and  54  described above, but a shallower height, reflecting the shallower depth of section of member  38  as compared to member  20 . Grommet  220  differs from grommet  60  primarily in the ratio of its altitude, or height, in plan view, as measured from base sidewall  238  to apex  240 . Thus sidewalls  242  and  244  are each shorter than base sidewall  238 , whereas base sidewall  112  is the shortest side of grommet  60 . A similar lengthening or shortening of aspect ratio permits a family of grommets to be manufactured suitable for a family of structural members sharing the same pitch between adjacent through-web openings. 
     Although structural member  22 , as shown in FIGS. 1 a ,  1   b , and  1   c  is preferred, other arrangements of flangework could be presented. For the purposes of the present invention it is not necessary that the flangework extend fully and continuously about the entire periphery of the opening. The flangework could, for example, extend only along the sides of the struts, and in the strut root portions. The flangework can be of varying height, or depth, about the periphery. The flangework can taper from a deepest section at the mid span of the struts to shallower portions adjacent the roots, or to taper into no flange at all, or could be formed only at the roots. 
     For example, in FIGS. 6 a  and  6   b  a structural member  250  has a lip flange  252  that is less sharply angled from web plane ‘W’ that that of structural member  20 . The openings defined in structural member  250  are more sharply triangular than opening  48 , having the form of equilateral triangles with a common radius of curvature at each corner. The radius at the free edge of the corner flange portions  254  is larger than at the plane of web ‘W’, yielding a relatively large, relatively shallowly angled corner web  256 . 
     In FIGS. 7 a  and  7   b  a structural member  260  is similar to structural member  250 , except insofar as it employs a steeper corner flange portion  262 . In FIGS. 8 a  and  8   b  a relatively heavy section structural member  270  had formed flanges  272  and  274 , and a deeper lip flange  274 , than member  250 . In FIG. 9 a  a structural member  276  has a lip flange  278  that is formed outwardly of the section, rather than inwardly as in FIG. 3 a ., such that the insertion direction of grommet  60  would tend to be reversed. In FIG. 9 b  a structural member  280  has asymmetric main flanges  282  and  284 . In FIG. 9 c  a structural member  286  has one flange  288  formed to one side of web plane ‘W’, and another flange  290  formed to the other side. Grommets such as grommet  60  or grommet  220 , depending on the size required, can be installed to co-operate with each of the illustrated sections noted above. 
     Further, although the preferred form of opening, and of grommet, is a form that is generally similar to an isosceles triangle with rounded corners, other shapes could be used. For example, a trapezoidal opening between the opposed margins of the web and a pair of diagonally inclined struts is also possible. As the radius of curvature of the apex corner increases, the resultant opening tends to take on a ‘D’-shaped appearance in plan view, particularly as the width of section increases relative to the base dimension of the opening, or as the radius of the apex approaches half the length of the base side. In general, the opening has a base portion adjacent to one margin of the web, and a pair of side portions that extend away from the base portion to meet at an apex adjacent to the other margin of the web. 
     Another type of roll-formed structural member is shown in FIGS. 10 a  and  10   b  as  300 . It has a web  302  having wide portions  304  alternating with narrow portions  306  to give a saw-tooth, or zig-zag appearance. One edge  308  of web  302  is straight while the other edge  310  undulates. Along edge  308  member  300  has a longitudinal main flange structure  312 . Along undulating edge  310  member  300  has a lip, or edge reinforcement flange  314  extending perpendicular to the plane of the web. 
     Triangular openings  316  are defined centrally in each of the wide portions of web  302 , each triangular opening  316  having a peripheral flange  318  and smoothly radiused base and altitudinal corners  320 ,  322  and  324 . Each triangular opening tends to divide its respective wide portion into a pair of tapering triangular struts  326  and  328  that meet at a point  330 . The flange  314  acts as an embedment formation for point  330 , but in addition point  330  also has defined in it, adjacent flange  314 , an aperture  332  through which a cast material such as concrete can flow. Further, as shown in FIG. 10 c , the embedment formation can include a tongue  334  that extends laterally from the web in the opposite direction from flange  314 , and can be formed from the blanked-out material removed to form aperture  332 . As illustrated in FIG. 10 a , the tip of point  330  is embedded in cast material  336  to a level lying between flange  314  and the altitudinal corner of flange  314 . A grommet, such as grommet  60  or grommet  220 , with suitable adjustments for size of opening and depth of flange to be captured, can be seated in opening  316 . As such, services carried through the grommet are carried in a controlled position, through the web, at a position between main flange  312  and flange  314 , through the controlled geometry of opening  316 . The geometry of opening  316  is controlled in the sense that it is determined by the shape of dies in a rotary press as the point of manufacture of the structural member. There may tend to be much less control over the dimension between flange  314  at the narrow throat  338  and the cast material. 
     Main flange  312  can be formed in a variety of configurations. As shown in FIG. 11 a  The main flange can be a triangular element  340 , or other tube shape, whether circular of polygonal. As shown in FIG. 11 b , the main flange  342  can be more or less channel-shaped, with a relatively large outboard leg  344 . As shown in FIG. 11 c  a main flange  346  can be a main flange  348  can be formed in the shape of an angle iron with a main leg  350  parallel to the cast material, and a small lip  352  at the outboard distal extremity. In FIGS. 12 a  and  12   b , a pair of structural members  360  and  362  having undulating edges are mounted back-to-back to form a beam having a pair of parallel main flanges  364  and  366 . As above, each has an opening  368  with a formed lip  370  to which a grommet such as grommet  60  or  220  can mount, thereby providing a controlled dimension protected passageway for carrying services. 
     Various embodiments of the invention have now been described in detail. Inasmuch as changes in and or additions to the above-described best mode may be made without departing from the nature, spirit or scope of the invention, the invention is not to be limited to those details, but only by the appended claims.