US3771272A

US3771272A - Flush mounting insert for sandwich panels

Info

Publication number: US3771272A
Application number: US00132745A
Authority: US
Inventors: M Mihaly; C Faroni
Original assignee: Amerace Corp
Current assignee: Harvard Industries Inc
Priority date: 1971-04-09
Filing date: 1971-04-09
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13
Also published as: IT951000B; FR2132812A1; GB1386806A; CA954431A; DE2216488A1; FR2132812B1

Abstract

A threaded insert to be installed flush with the surface of an outer sheet of a sandwich panel and to be secured in the panel by a hardenable liquid adhesive, the insert having a flange at one end thereof with a tapered, threaded peripheral edge surface, which engages and positively grips the outer sheet along the corresponding edge of an opening in the sheet, through which opening the insert has been installed, so as to retain the insert in place within the sandwich panel, with the flange flush with the surface of the outer sheet, while the adhesive hardens.

Description

United States Patent [1 1 Mihaly et al.

[ Nov. 13, 1973 1 FLUSH MOUNTING INSERT FOR SANDWICH PANELS [75] Inventors: Michael F. Mihaly, Madison;

Charles C. Faronl, Summit, both of NJ.

[73] Assignee: Amerace Esna Corporation, New

York, N.Y.

22 Filed: Apr. 9, 1971 21 Appl.No.:132,745

[52] US. Cl 52/617, 52/366,151/4l.73

[51] Int. Cl. F16b 39/282 [58] Field of Search 52/617, 621; l5l/41.7, 41.73

[56] References Cited UNITED STATES PATENTS 3,646,981 3/1972 Barnes 52/617 3,297,071 1/1967 Neuschotz et a1. l5l/4l.73

2,880,830 4/1959 Rohe l5l/4l.7

2,967,448 1/1961 Hallock 151/4173 3,451,181 6/1969 Neuschotz 52/617 3,282,015 11/1966 R0116 et a1. 52/617 3,313,078 4/1967 Rohe 52/617 3,019,865 2/1962 Rohe..... 52/617 3,434,261 3/1969 Rohe 52/617 Primary Examiner-Frank L. Abbott Assistant ExaminerLeslie A. Braun Attorney-Samuelson & Jacob [57] ABSTRACT A threaded insert to be installed flush with the surface of an outer sheet of a sandwich panel and to be secured in the panel by a hardenable liquid adhesive, the insert having a flange at one end thereof with a tapered, threaded peripheral edge surface, which engages and positively grips the outer sheet along the corresponding edge of an opening in the sheet, through which opening the insert has been installed, so as to retain the insert in place within the sandwich panel, with the flange flush with the surface of the outer sheet, while the adhesive hardens.

8 Claims, 7 Drawing Figures PATENTEDHuvmm 3,771,272 SHEET 10F 3 INVENTORS MICHAEL E MlHaue CHARLES 6 FR RONI PAIENIEDHUV 13 mu 3.771,. 2 2.

SHEET 2 OF 3 INVENTORs MICHAEL E Mu-mue 40 74 46 42 2 BY CHHRLES C Fmzom HTTOJQ? PATENIEUHUV 13 I975 SHEET 38F 3 r 5 146 l llllllll uiiiiiii INVENTOR-S Mucuaa. E Mwmu CHARLES C. Fmzom HTTO FLUSH MOUNTING INSERT FOR SANDWICH PANELS The present invention relates generally to fasteners which are to be affixed to sandwich panels, such as those panels known as honeycomb cored structures, and pertains, more specifically, to threaded inserts having a structure which enables these inserts to be installed quickly and anchored effectively flush with the panel surface.

The increased demand for high-strength, lightweight panels has led to the increased use of honeycomb cored panels as a means for meeting such requirements. Screw-threaded inserts have been employed in connection with such panels where it is necessary to provide some means for either fastening other structural elements to a panel or fastening the panel to another supporting structure.

Since the structural components of a honeycomb panel usually include a honeycomb core of relatively thin material sandwiched between a pair of thin facial sheets, problems arise in finding some means for effectively anchoring inserts within these sandwich panels without failure of any of the components of the panel during installation or use of the inserts.

It has been proposed to anchor threaded inserts within sandwich panels by filling a cavity in the panel with a synthetic resin material and then anchoring the insert in the synthetic resin. Such an arrangement allows synthetic resin to become affixed to the honeycomb core, as well as to the facial sheets, to establish an advantageous distribution of the stresses applied to the insert.

In some of these proposals, the cavity is first filled with a liquid synthetic resin which is then allowed to harden. The hardened material is then drilled and an insert is anchored in the drilled hole. Such a procedure requires a multiplicity of operations and occasions a delay in the sequence of operations since the resinous material must be given time to harden between the filling and drilling operations.

In other proposals, the insert is placed within the cavity and an adhesive, generally in the form of a synthetic resin material, is injected, in liquid form, into the cavity around the insert and is allowed to harden. Such proposals require relatively elaborate installation tools and equipment and present a problem in assuring that the insert is aligned properly relative to the panel as the resinous material hardens.

In still further proposals, synthetic resin material is placed within the cavity, in liquid form, and, before the material can harden, an insert is embedded in the resinous material. Subsequently, the resinous material hardens to permanently anchor the insert within the panel. Such proposals have suffered from the difficulty of keeping the insert in proper alignment within the cavity upon installation and while the resinous material is hardening and the possibility that the unhardened resinous material can flow out of the cavity either during installation of the insert or after such installation and prior to hardening.

In an effort to overcome the various drawbacks out-- lined above, inserts have been developed which, upon installation in a sandwich panel, engage the upper facial sheet through which the insert is passed in such a way that the insert closes the opening in the facial sheet to prevent escape of the liquid resonous material while at the same time maintaining proper alignment of the insert in the cavity. However, the same structure which enables these inserts to attain the above advantages also precludes installation of the insert flush with the outer surface of the facial sheet.

It is therefore an importnat object of the invention to provide an insert for sandwich panels, which insert is to be installed within a cavity in the panel, flush'with the outer surface of the panel, after placing liquid adhesive material within the cavity, but before the adhesive material hardens, and which can be aligned properly relative to the panel during installation and will remain in such alignment while the adhesive hardens.

Another object of the invention is to provide an insert as set forth above which tends to preclude escape of adhesive from the cavity prior to hardening of the adhesive.

Still another object of the invention is to provide an insert which is easily installed without complex equipment and without elaborate, time-consuming procedures.

A further object of the invention is to provide an insert having a simplified construction which is easily and inexpensively fabricated in large quantities of uniform quality.

The above objects, as well as still further objects and advantages, are attained by the invention which may be described briefly as an insert for providing fastener means in a sandwich panel having opposite facial sheets of prescribed thickness and a cavity between the sheets for receiving the insert and a hardenable liquid adhesive prior to insertion of the insert, the cavity including an opening of predetermined diameter in one of the sheets, the insert comprising a body having opposite ends and a central longitudinal axis, fastener means in the body for receiving a mating fastener member, a flange projecting radially from the body and having a radial surface and an outer peripheral edge surface with a diameter corresponding to the diameter of the opening and an axial extent at least of the order of magnitude of the thickness of the one sheet, and a thread on the peripheral edge surface, the thread having a pitch no greater than approximately the thickness of the one sheet, the peripheral edge surface being tapered from a larger diameter at the radial surface to a smaller diameter toward the other end of the body such that the pitch line of the thread on the peripheral edge surface makes an acute angle with the longitudinal axis of the body.

The invention will be more fully understood while still further objects and advantages will become apparent in the following detailed description of preferred embodiments of the invention illustrated in the accompanying drawing, in which:

FIG. 1 is an elevational view, partially sectioned, illustrating an insert constructed in accordance with the invention about to be installed within a sandwich panel;

FIG. 2 is a top plan view of the insert;

.FIG. 3 is a bottom plan view of the insert;

FIG. 4 is an elevational view similar to that of FIG. 1 with the insert installed in the sandwich panel and a complementary threaded fastener installed in the insert;

FIG. 5 is an elevational view, partially sectioned, illustrating another insert constructed in accordance with the invention;

FIG. 6 is a bottom plan of the insert of FIG. 5; and

FIG. 7 is an elevational view, partially sectioned, illustrating still another insert constructed in accordance with the invention.

Referring now to the drawing, and especially to FIGS. 1 through 3 thereof, there is illustrated an insert 10 constructed in accordance with the invention, the insert having a body 12 with

opposite ends

14 and 16 and fastener means for receiving a mating fastener member in engagement with the body. The body 12 is in the form of a tubular member 20, which is preferably fabricated of a metal, such as steel or aluminum. The fastener means is shown in the form of an internally threaded aperture 22 extending axially in the tubular member 20, the aperture 22 being open at the upper end 14 for the reception of a mating externally threaded member such as a screw or bolt, and being closed at the lower end 16 by means of a plug 24 permanently affixed within an annular seat 26 in the tubular member by means of a lip 28 overlapping the plug 24.

The body 12 of the insert 10 is provided with a flange 30 projecting radially from the body at the upper end 14, the flange 30 having an uppermost radial surface 32 and an outer peripheral edge surface 34. The outer peripheral edge surface 34 is provided with a thread 36 and is tapered from a larger diameter at the uppermost radial surface 32 to a smaller diameter at the underside 38 of the flange 30 for purposes which will be described more fully hereinafter.

Adjacent the lower end 16 of the body 12 of insert 10 there is provided another flange 40 which projects radially outwardly from the body and which includes a plurality of notches 42 extending radially intothe lower flange 40 from the perimeter 44 thereof, the notches including opposite side-walls 46.

Insert 10 is to be installed within a sandwich panel 50 which has upper and lower

facial sheets

52 and 54, respectively, affixed to a honeycomb core 56. A cavity 58 has been provided within the panel 50 and an opening 60 has been made through the upper facial sheet 52 and communicates with the cavity 58. As seen in FIG.

1, a hardenable adhesive 62, in liquid form, such as, for example, an epoxy resin, has beeen deposited in the cavity 58 just prior to the insertion of the insert 10. The opening 60 is circular and has a diameter large enough to admit the lower end 16 ofthe insert 10 and the lower flange 40 into the cavity 58. However, the diameter of the opening 60 is somewhat smaller than the overall diameter of the upper flange 30, hence, further advancement of the insert 10 into the cavity 58 is accomplished by rotating the insert about the central longitudinal axis L thereof.

As best seen in FIG. 4 such rotation of the insert 10 will enable the thread 36 to positively grip the upper facial sheet 52 along the peripheral edge 64 of the opening 60 therein and, by virtue of the formation of a corresponding complementary thread 65 in the upper facial sheet 52 along the edge 64 of the opening 60 therein, such rotation of the flange 30 relative to the opening 60 will advance the insert 10 into the cavity 58 until the uppermost radial surfaces 32 of the flange 30 becomes generally parallel with uuper facial sheet 52 and essentially flush with the upper surface 66 of the sheet 52. The positive grip of the outer peripheral edge surface 34 of the flange 30 upon the upper facial sheet 52 will then serve to hold the insert 10 in place in the cavity 58 in proper alignment therewith while the adhesive 62 hardens.

The upper flange 30 has a thickness, at least at the peripheral edge sufrace 34, of at least approximately the thickness of the sheet 52 with which it is engaged and is illustrated slightly thicker than the sheet 52 to assure a secure engagement between the peripheral edge surface 34 of the flange 30 and the corresponding edge 64 of the opening in the sheet. Such an engagement not only retains the insert 10 in proper alignment within the cavity 58 while the adhesive 62 is hardening, but also serves to seal the opening 60 against leakage of the liquid adhesive 62 from the cavity 58 through the opening 60 after the insert 10 is inserted and while the adhesive is hardening. The tapered configuration of the peripheral edge surface 34 facilitates proper engagement of the flange 30 with the opening 60 and alignment of the insert 10 within the cavity 58 while also serving to accommodate dimensional variations in the opening 60.

The thread 36 follows the tapered configuration of the peripheral edge surface 34 of the flange 30, the pitch line P of the thread 36 making an acute angle A with the longitudinal axis L of the body 12. Thus, thread 36 is actually in the form of a spiral in that the diameter of the thread decreases as the thread is followed from radial surface 32 toward underside 38. The particular spiral form of thread 36 enables the thread to grip the relatively thin peripheral edge of the opening 60 and establish a complementary thread in the opening 60 which assures that the insert 10 will be properly advanced and aligned upon installation and then retained in place until the adhesive hardens.

The pitch of thread 36 is relatively small and is preferably no greater than approximately the thickness of the sheet 52 so that at least one complementary thread will be established in the edge of opening 60. The thickness of the upper facial sheet 52 of typical honeycomb panels now in common use varies from approximately 0.014 inch to 0.040 inch. Hence, a typical pitch for thread 36 is about 0.0138 inch, somewhat less than the thinnest facial sheet of a panel in which the insert is to be installed. In inserts constructed for use in such typical panels, the acute angle A is preferably in the order of magnitude of 12.

In order to facilitate rotation of the upper flange 30, together with the body 12 of the insert 10 itself, the flange 30 is provided with at least two recesses 68 extending axially into the flange from the uppermost radial surface 32 for accommodating the cooperative engagement of complementary rotating means in the form of a wrench or like tool illustrated at 70 and having corresponding projections 71 which can be received within the recesses 68 to rotate and drive the insert 10 into the cavity 58 until the lowermost surface 72 of the flange 73 of tool 70 contacts the upper facial sheet 52 and the uppermost radial surface 32 is renthe adhesive 62 for anchoring the insert between the sheets when the adhesive hardens. In addition, the adhesive 62 will establish a bond between the lower flange 40 and the lower facial sheet 54 of the panel 50 by virtue of a small clearance between the lowermost lateral surface 74 of the flange 40 and lower sheet 54 which enables adhesive 62 to effect such a bond. Resistance to rotation of the insert relative to the panel 50 upon hardening of the adhesive 62 is enhanced by the notches 42 in the flange 40, which will become filled with adhesive upon insertion of the insert, by virtue of the keying effect of the solidified adhesive 62 within the notches 42. Alternative means for precluding such rotation of the insert may be provided by flats on the flange 40, rather than notches, or a similar structure which will interengage the solidified adhesive.

As best seen in FIGS. 1, 2 and 4, the tubular member of the body 12 is deformed radially inwardly at diametrically opposite areas 76. These areas 76 of inward deformation radially constrict the threaded aperture 22 adjacent the lower end 16 of the body 12 and serve as a screw stop. Thus, as seen in FIG. 4, upon installation of a complementary threaded fastener member 80 into the threaded aperture 22 of the insert 10, the complementary fastener member'80 may be advanced only until the end 82 of the member abuts the deformed areas 76, at which point the complementary threaded member 80 will be inhibited from abutting the plug 24 at the bottom of the aperture 22. Thus, the complementary threaded member 80 is precluded from abutting and possibly pushing against the plug 24. Dislocation or bulging out of the plug 24 could cause undesirable bulging out of the lower facial sheet 54 with concomitant deleterious effects upon the aesthetic appearance of the outer face 84 of the sheet 54.

Turning now to FIGS. 5 and 6, another insert constructed in accordance with the invention is illustrated generally at 1 l0 and is seen to have a construction similar to insert 10. Thus, insert 100 also includes a body 112 having a threaded aperture 1 14 therein and including an upper flange 116 projecting radially from the upper end 118 of the body 112 and a lower flange 120 projecting radially from the lower end 122 of the body. The upper flange .116 has an uppermost radial surface 124 terminating in a peripheral edge surface 128 which, as in the earlier-described embodiment, is provided with a spiral thread 130 which progresses from a larger diameter at uppermost radial surface 124 to a smaller diameter at the underside 132 of the flange 116.

In this instance, however, the threaded aperture 114 terminates short of the lower end 122 of the body 112 so that the remaining portion 134 of the body 112 serves as the means which closes the aperture 114 at the bottom end of the body. In addition, the potrion 134 serves as a screw stop to preclude deleterious downward movement of a mating threaded fastener inserted into the threaded aperture 114.

It is noted that the upper flange 1 16 ofinsert 1 10, unlike the corresponding flange 30 of insert 10, does not contain wrenching recesses which would correspond to recesses 68 of insert 10. Thus, insert 110 may be engaged by a tool 140 having a threaded extension 142 which is to be received within threaded aperture 114 until the lowermost surface 114 of a flange 146 on the tool 140 is seated upon upper surface 124 of insert 110.

Further turning of the tool 140 will then enable the thread to engage an opening in the panel within which the insert is to be installed. Upon completion of the installation, the tool may be retracted by reverse rotation.

The lower flange 120 is provided with means for engaging the hardened adhesive to impede rotation of the insert, in this instance the means being in the form opposite flats 150 on the perimeter of the flange 120.

Referring now to FIG. 7, still another embodiment of the invention is illustrated in the form of insert 210 having a body 212 with an upper flange 214 projecting radially from the upper end 216 of the body 212 and a lower flange 218 projecting radially from the lower end 220 of the body. The upper flange 214 has an uppermost radial surface 222 terminating in a peripheral edge surface 224, which, as in the earlier-described embodiments, is provided with a spiral thread 226 progressing from a larger diameter at the uppermost radial surface 222 to a smaller diameter at the underside 228 of the flange 214.

Body 212 of insert 210 is provided with an aperture 230 which is closed at the lower end thereof by a plug member 232 affixed within a recess 234 in the lower flange 218. An internally threaded sleeve 236 is placed within the aperture 230 to provide the body 212 with an internally threaded fastener means capable of receiving a complementary externally threaded fastener member (not shown). The threaded sleeve 236 is itself provided with a radial flange 238 which projects into an enlarged portion 240 of the aperture 230 to retain the sleeve 236 within the body 212 of the insert 210. Rotation of the sleeve 236 relative to the body 212 is precluded by a key 242 which engages a corresponding slot 244 in the flange 238. Since there is some clearance between the sleeve 236 and the walls of the aperture 230, a certain amount of radial float is permitted to thereby facilitate alignment of the internal threads of the insert 210 with a mating threaded fastener.

As in the earlier-described insert 10, the present insert 210 includes a pair of opposite recesses 250 in the upper flange 214 for facilitating installation of the insert, and the lower flange 218 is provided with notches 252 for precluding rotation of the insert once the adhesive is hardened.

Threaded sleeve 236 may be permanently deformed radially inwardly at 254 to provide the thread thereof with a prevailing torque type self-locking mechanism of a now well-known variety. Likewise, the body of either of the

insert

10 or 110 may be so deformed to provide the threaded apertures of those inserts with such a selflocking mechanism.

It is to be understood that the above detailed description of preferred embodiments of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as set forth in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An insert for providing fastener means in a sandwich panel having opposite facial sheets of prescribed thickness and a cavity between the sheets for receiving the insert and a hardenable liquid adhesive prior to insertion of the insert, said cavity including an opening of predetermined diameter in one of said sheets, said insert comprising:

a body having opposite ends and a central longitudinal axis;

fastener means in said body for receiving a mating fastener member;

a flange projecting radially from the body and having a radial surface and an outer peripheral edge surface with a diameter corresponding to the diameter of said opening and an axial extent substantially greater than the thickness of said one sheet;

a thread on the peripheral edge surface, said thread having a pitch substantially less than the axial extent of said peripheral edge surface, said peripheral edge surface being tapered from a larger diameter at said radial surface to a smaller diameter toward the other end of the body such that the pitch line of the thread on the peripheral edge surface makes an actue angle with the longitudinal axis of the body;

a second flange soaced from the first and flange and extending radially from said body in order to extend into said adhesive for anchoring said insert between the sheets; and

means on the second flange for engaging the adhesive to impede rotation of the insert when the adhesive hardens.

2. The insert of claim 1 wherein said acute angle is in the order of magnitude of 12.

3. The insert of claim 1 wherein the flange includes at least two recesses extending axially from said radial surface into the flange for enabling the cooperative engagement of complementary rotating means.

4. An insert for providing fastener means in a sandwich panel having opposite facial sheets of prescribed thickenss and a cavity between the sheets for receiving the insert and a hardenable liquid adhesive prior to insertion of the insert, said cavity including an opening of predetermined diameter in one of said sheets, said insert comprising:

a body having opposite ends, a central longitudinal axis, and an aperture extending axially into said body between said opposite ends;

an internal screw thread engageable with a complementary externally threaded member inserted into said aperture;

means closing said aperture adjacent one of the opposite ends of the body;

a flange projecting radially from the body adjacent the other of said opposite ends thereof, said flange having a radial surface at said other end of the body and an outer peripheral edge surface with a diameter corresponding to the diametero of said opening and an axial extent of at least approximately the thickness of said one sheet;

an axially extending spiral thread in the peripheral edge surface of the flange, said spiral thread decreasing in diameter from a larger diameter at the radial surface to a smaller diameter toward said one of the opposite ends and having a pitch no greater than approximately the axial extent of said peripheral edge surface, said thread being capable of forming a corresponding complementary thread in said one sheet along the opening therein in response to rotation of said flange relative to said one sheet such that said flange can grip said one sheet and retain the insert in place, with the radial surface essentially flush with the outer surface of said one sheet, as the adhesive hardens;

a second flange spaced from the first said flange and extending radially from said body in order to extend into said adhesive for anchoring said insert between the sheets; and

means on the second flange for engaging the adhesive to impedg rotation of the insert when the adhesive hardens.

5. The insert of claim 4 including at least one radial constriction in said aperture immediately adjacent said aperture closing means so as to inhibit the passage of the complementary externally threaded member into said aperture beyond said radial constriction.

6. The insert of claim 4 wherein the axial extent of the peripheral edge surface is substantially greater than the thickness of said one sheet and the pitch of said thread is substantially less than the axial extent of the peripheral edge surface.

7. The insert of claim 6 wherein the pitch line of the spiral thread makes an acute angle in the order of magnitude of 12 with the longitudinal axis of the body.

8. The insert of claim 4 wherein the flange includes at least two recesses extending axially from said radial surface into the flange for enabling the cooperative engagement of complementary rotating means UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,771,272 Dated Noyember 13. 1973 Inventor(s) Michael F. Mihaly et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, last line, "resonous" should read -resinous- Column 2, line 6, "importnat" should read -important Column 3, line 43, "beeen" should read -been- Column 3, line 62, "uuper" should read -upper-- Column 4, line 4, "sufrace" should read surface- Column 4 line 66, "betweem" should read --between- Column 5, line 39, "100" should read -ll0- Column 5, line 55, "potrion" should read -portion- Claim 1, Column 7, line 19, "actue" should read -acute- Claim 1, Column 7, line 21, "soaced" should read ---spaced- Claim 4, Column 7, line 36, "thickenss" should read -thickness Claim 4, Column 8, line 6, "diametero" should read -diameter-- Claim 4, Column 8, line 28, "impedg" should read -impede- Claim 8, Column 8, line 46, "means" should read -means.

Signed and sealed this 25th day of June 197L (SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Comiasioner of Patents FORM PO-1050 (10-69) USCOMM,DC 5o376 P9 uus. GOVERNMENT PRINTING orncz: I969 0-366-32.

Claims

1. An insert for providing fastener means in a sandwich panel having opposite facial sheets of prescribed thickness and a cavity between the sheets for receiving the insert and a hardenable liquid adhesive prior to insertion of the insert, said cavity including an opening of predetermined diameter in one of said sheets, said insert comprising: a body having opposite ends and a central longitudinal axis; fastener means in said body for receiving a mating fastener member; a flange projecting radially from the body and having a radial surface and an outer peripheral edge surface with a diameter corresponding to the diameter of said opening and an axial extent substantially greater than the thickness of said one sheet; a thread on the peripheral edge surface, said thread having a pitch substantially less than the axial extent of said peripheral edge surface, said peripheral edge surface being tapered from a larger diameter at said radial surface to a smaller diameter toward the other end of the body such that the pitch line of the thread on the peripheral edge surface makes an actue angle with the longitudinal axis of the body; a second flange soaced from the first and flange and extending radially from said body in order to extend into said adhesive for anchoring said insert between the sheets; and means on the second flange for engaging the adhesive to impede rotation of the insert when the adhesive hardens.

2. The insert of claim 1 wherein said acute angle is in the order of magnitude of 12*.

4. An insert for providing fastener means in a sandwich panel having opposite facial sheets of prescribed thickenss and a cavity between the sheets for receiving the insert and a hardenable liquid adhesive prior to insertion of the insert, said cavity including an opening of predetermined diameter in one of said sheets, said insert comprising: a body having opposite ends, a central longitudinal axis, and an aperture extending axially into said body between said opposite ends; an internal screw thread engageable with a complementary externally threaded member inserted into said aperture; means closing said aperture adjacent one of the opposite ends of the body; a flange projecting radially from the body adjacent the other of said opposite ends thereof, said flange having A radial surface at said other end of the body and an outer peripheral edge surface with a diameter corresponding to the diametero of said opening and an axial extent of at least approximately the thickness of said one sheet; an axially extending spiral thread in the peripheral edge surface of the flange, said spiral thread decreasing in diameter from a larger diameter at the radial surface to a smaller diameter toward said one of the opposite ends and having a pitch no greater than approximately the axial extent of said peripheral edge surface, said thread being capable of forming a corresponding complementary thread in said one sheet along the opening therein in response to rotation of said flange relative to said one sheet such that said flange can grip said one sheet and retain the insert in place, with the radial surface essentially flush with the outer surface of said one sheet, as the adhesive hardens; a second flange spaced from the first said flange and extending radially from said body in order to extend into said adhesive for anchoring said insert between the sheets; and means on the second flange for engaging the adhesive to impedg rotation of the insert when the adhesive hardens.

7. The insert of claim 6 wherein the pitch line of the spiral thread makes an acute angle in the order of magnitude of 12* with the longitudinal axis of the body.

8. The insert of claim 4 wherein the flange includes at least two recesses extending axially from said radial surface into the flange for enabling the cooperative engagement of complementary rotating means