U.S. patent application number 14/330462 was filed with the patent office on 2014-10-30 for floating captive screw.
This patent application is currently assigned to Southco, Inc.. The applicant listed for this patent is Southco, Inc.. Invention is credited to Thomas V. AUKZEMAS, Joseph N. Caulfield, Albert J. Frattarola, James F. Standish, III, Boyd Wolf.
Application Number | 20140321942 14/330462 |
Document ID | / |
Family ID | 33096652 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140321942 |
Kind Code |
A1 |
AUKZEMAS; Thomas V. ; et
al. |
October 30, 2014 |
FLOATING CAPTIVE SCREW
Abstract
A captive screw for securing together two panels has a screw and
a spring extending between the screw head and a ferrule. A collar
is formed on the screw shank under the ferrule to limit penetration
of the screw threads in a bottom panel so that the upper panel
floats on the spring.
Inventors: |
AUKZEMAS; Thomas V.;
(Wilmington, DE) ; Frattarola; Albert J.; (Glen
Mills, PA) ; Wolf; Boyd; (Chadds Ford, PA) ;
Standish, III; James F.; (Kennett Square, PA) ;
Caulfield; Joseph N.; (Aston, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Southco, Inc. |
Concordville |
PA |
US |
|
|
Assignee: |
Southco, Inc.
Concordville
PA
|
Family ID: |
33096652 |
Appl. No.: |
14/330462 |
Filed: |
July 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11856577 |
Sep 17, 2007 |
8794889 |
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14330462 |
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10364828 |
Feb 10, 2003 |
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11856577 |
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09803221 |
Mar 9, 2001 |
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10364828 |
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60188406 |
Mar 10, 2000 |
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Current U.S.
Class: |
411/353 |
Current CPC
Class: |
F16B 41/002 20130101;
Y10S 411/999 20130101; F16B 35/041 20130101; F16B 31/04 20130101;
F16B 5/0266 20130101 |
Class at
Publication: |
411/353 |
International
Class: |
F16B 41/00 20060101
F16B041/00 |
Claims
1. A captive screw configured to attach a first panel to a second
panel comprising: a ferrule having a bore; a screw having a head, a
shank extending from the head, a threaded portion at an end of the
shank opposite the head, and a collar on the shank proximate the
threaded portion; and a spring, wherein the shank extends through
the bore and the spring, such that the spring is between the
ferrule and the head of the screw, wherein the bore includes at
least one diameter and the collar includes a maximum diameter, the
maximum diameter is greater than the at least one diameter of the
bore, and the at least one diameter of the bore is located between
the maximum diameter of the collar and the head of the screw, and
wherein the collar is configured to limit penetration of the
threaded portion into the second panel, so that the first panel,
when attached to the ferrule, floats on the spring.
2. A captive screw according to claim 1, wherein the ferrule
includes an inner annular ring extending from an internal
circumferential surface of the ferrule and the inner annular ring
provides the at least one diameter of the bore.
3. A captive screw according to claim 2, wherein the ferrule has at
least one collapsed groove in an external circumferential surface
of the ferrule.
4. A captive screw according to claim 1, wherein the ferrule has an
end portion configured to be flared to retain the ferrule on the
first panel.
5. A captive screw according to claim 1, wherein the ferrule has an
end portion configured to be bent upwardly to form an inner annular
ring by plastic deformation of ferrule material, and the inner
annular ring provides the at least one diameter of the bore.
6. A captive screw according to claim 1, wherein the ferrule
includes an annular lip configured to limit penetration of the
ferrule into the first panel.
7. A captive screw according to claim 6, wherein at least one
circumferential groove on an external surface of the ferrule is
configured to receive material of the first panel when the ferrule
is pressed into the first panel.
8. A captive screw according to claim 7, wherein the at least one
circumferential groove is adjacent to the annular lip, and the
annular lip is between the at least one circumferential groove and
the head of the screw.
9. A captive screw according to claim 1, wherein at least one
circumferential groove on an external surface of the ferrule is
configured to receive material of the first panel when the ferrule
is pressed into the first panel.
10. A captive screw according to claim 1, wherein an external
circumferential surface of the ferrule includes a plurality of
knurls.
11. A captive screw according to claim 1, wherein the collar is
tapered.
12. A heat dissipating system comprising: a first panel comprising
a heat sink, a second panel comprising a PC board, and a captive
screw attached to the first panel and the second panel, wherein the
captive screw comprises a ferrule having a bore; a screw having a
head, a shank extending from the head, a threaded portion at an end
of the shank opposite the head, and a collar on the shank proximate
the threaded portion; and a spring, wherein the shank extends
through the bore and the spring, such that the spring is between
the ferrule and the head of the screw, and wherein the bore
includes at least one diameter and the collar includes a maximum
diameter, the maximum diameter is greater than the at least one
diameter of the bore, and the at least one diameter of the bore is
located between the maximum diameter of the collar and thehead of
the screw, and wherein the threaded portion is inserted into the
second panel, the collar contacts the second panel, the ferrule is
attached to the first panel, and the first panel floats on the
spring.
13. A heat dissipating system according to claim 12, wherein the
ferrule includes an inner annular ring extending from an internal
circumferential surface of the ferrule, and the inner annular ring
provides the at least one diameter of the bore.
14. A heat dissipating system according to claim 13, wherein the
ferrule has at least one collapsed groove in an external
circumferential surface of the ferrule.
15. A heat dissipating system according to claim 12, wherein the
end portion is flared to retain the ferrule on the first panel.
16. A heat dissipating system according to claim 12, wherein the
ferrule includes an annular lip that limits penetration of the
ferrule into the first panel.
17. A heat dissipating system according to claim 12, wherein the
ferrule includes at least one circumferential groove and material
of the first panel is located within the at least one
circumferential groove.
18. A heat dissipating system according to claim 12, wherein an
external circumferential surface of the ferrule includes a
plurality of knurls.
19. A heat dissipating system according to claim 12, wherein the
collar is tapered.
20. A heat dissipating system according to claim 12 further
comprising a sheet of flexible material between the first and
second panels.
21. A floating captive screw capable of being mounted in a
preformed first aperture of a first panel, being a microcircuit
heat sink flange, for attachment to a second aperture in a second
panel, being a PC board, said captive screw comprising: a ferrule
having a generally cylindrical portion having an inner bore, said
ferrule being adapted to be received into said first aperture of
said first panel; a screw having a head, a shank and a threaded
portion at the end of the shank opposite the head, said shank and
said threaded portion being adapted to pass through said ferrule
bore; a collar being fixed on said shank at a position between said
ferrule and the screw threaded portion after said screw shank and
said threaded portion have passed through the ferrule bore, wherein
said collar limits penetration of the screw when engaging said
second panel and wherein said collar captivates said screw to said
ferrule; a spring positioned over said screw shank between said
head and said ferrule; wherein said collar is formed by being
rolled onto said screw shank under the ferrule to limit penetration
of the screw threads in the second panel so that the first panel
floats on the spring; wherein the ferrule has an annular lip formed
on an exterior cylindrical surface proximate the top of the ferrule
for limiting the penetration of the ferrule in the preformed
aperture in the first structure, and the ferrule has an annular
circumferential groove formed in the exterior cylindrical surface
adjacent to and below the annular lip for receiving a plastic flow
of material when the ferrule is pressed into a preformed
aperture.
22. A captive screw comprising: a ferrule having a first and a
second opposed ends, the ferrule having: a first annular lip at one
of the first and second opposed ends; an annular circumferential
exterior groove adjacent the first annular lip; and a second
annular lip adjacent to the annular circumferential exterior groove
and located across the annular circumferential exterior groove with
respect to the first annular lip; a screw having a head, a shank
adapted to pass through the ferrule, a threaded portion at one end
of the shank opposite the head, the shank having a collar, the
collar being fixed on the shank between the ferrule and the
threaded portion of the shank; and a spring extending on the shank
of the screw between the head and the ferrule; wherein the screw is
captivated on the ferrule between the head and the collar, and the
ferrule is dimensioned such that the ferrule does not permit
movement of the collar past the ferrule.
23. The captive screw according to claim 22 wherein the ferrule has
a generally cylindrical interior surface.
24. A floating captive screw capable of being mounted in a
preformed first aperture of a first panel, being a microcircuit
heat sink flange, for attachment to a second aperture in a second
panel, being a PC board, said captive screw comprising: a ferrule
having a generally cylindrical portion having an inner bore with an
inner annular ring on an interior surface of said bore, said
ferrule being adapted to be received into said first aperture of
said first panel; a screw having a head, a shank and a threaded
portion at the end of the shank opposite the head, said shank and
said threaded portion being adapted to pass through said ferrule
bore; wherein said inner annular ring is formed by plastic
deformation of material during assembly wherein pressure is applied
uniformly on the exterior of the generally cylindrical portion of
the ferrule to form said inner annular ring, wherein said ferrule
has a first annular circumferential groove which allows the
formation of the ring; a collar being fixed on said shank at a
position between said inner annular ring of said ferrule bore and
the screw threaded portion after said screw shank and said threaded
portion have passed through the ferrule bore, wherein said collar
limits penetration of the screw when engaging said second panel and
wherein said collar captivates said screw to said ferrule; a spring
positioned over said screw shank between said head and said inner
annular ring; wherein said collar is formed by being rolled onto
said screw shank under the ferrule to limit penetration of the
screw threads in the second panel so that the first panel floats on
the spring; wherein the ferrule has an annular lip formed on an
exterior cylindrical surface proximate the top of the ferrule for
limiting the penetration of the ferrule in the preformed aperture
in the first structure, and the ferrule has a second annular
circumferential groove formed in the exterior cylindrical surface
adjacent to and below the annular lip for receiving a plastic flow
of material when the ferrule is pressed into a preformed aperture.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/856,577, filed Sep. 17, 2007, which is a
continuation of U.S. patent application Ser. No. 10/364,828, filed
Feb. 10, 2003, which is continuation-in-part of U.S. patent
application Ser. No. 09/803,221, filed Mar. 9, 2001, which claims
the benefit of U.S. Provisional Application for Patent Ser. No.
60/188,406, filed Mar. 10, 2000, the contents of all of which are
incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to captive
screws.
BACKGROUND OF THE INVENTION
[0003] Captive screws are screws that are "captivated" or held
within a collar or ferrule. The ferrule is mounted in a first panel
or like object. The screw portion is captivated so that it can be
moved perpendicular to the first panel and the screw's threads can
engage a corresponding aperture in a second panel, so that the
first and second panels can be secured together. However, when the
panels are unscrewed and disengage, the screw is retained in the
first panel, Captive screws are useful in applications where it is
important to avoid dropping or losing screws during assembly or
repair, such as electronic devices, where a lost screw can cause
catastrophic electrical shorts damaging equipment.
[0004] One particular application for captive screws is to hold
down a heat sink which is mounted on top of a microchip and is
intended to dissipate the heat of the microchip. The microchip, in
turn, is fastened to a circuit board. Oftentimes, between the heat
sink and the microchip a compressible or elastic material in the
form of the sheet is placed. If one were to put the heat sink
directly on top of the microchip, there would be tiny gaps between
the two. Since air conducts heat poorly, these gaps have a
detrimental effect on heat transfer. This interface material in the
form of a sheet is needed and the sheet has a high thermal
conductivity. Recently, microchips during operation have been
getting warmer and warmer as space has been getting more and more
limited on circuit boards. Accordingly, heat sinks have been
getting larger and larger as the requirements for withstanding
vibrations has been getting more stringent. Standoffs have been
used which rise from the board to which the heat sinks are screwed
down. Difficulties encountered with standoffs have been that the
standoffs do not compensate for chip height variation and they do
not provide consistent compression of the interface material
between the chip and the heat sink.
[0005] In the past, various clamps, latches, pins, etc have been
used to hold heat sinks down. Plastic clips have been used,
however, this requires that the use of a screwdriver to screw in
the clip directly onto the circuit board which makes the board
susceptible to damage. Plastic clips, although they are not costly,
are limited by the weight of the heat sink and the clips have
proven to be unreliable in vibration and drop shock testing. Some
varieties of clips are clipped onto the heat sink at the ends of
fins in the middle of the heat sink. Unfortunately, the middle fins
are the most important fins in a heat sink as they carry most of
the heat load. Therefore, when such clips are used the need for a
larger heat sink results.
[0006] Accordingly, a need exists for a captive screw which is
captive or fixed to a first panel such as a heat sink whereby a
collar on the screw bottoms out at a fixed distance on a lower
panel when the screw is screwed into the lower panel thereby
allowing the captive screw to provide a constant pressure on the
top panel. In addition, the captive screw should be able to pass
stringent vibration testing and be able to allow for thermal
expansion.
[0007] The present invention has been developed in view of the
foregoing and to overcome the deficiencies of the prior art.
SUMMARY OF THE INVENTION
[0008] The present invention solves the problem of providing for
secure fastening of a lower panel to an upper panel while providing
a constant pressure on an upper panel to which the captive screw is
captive.
[0009] In one embodiment of the present invention, a captive screw
is disclosed which includes a ferrule, a screw, and a spring. The
screw has a head, a shank adapted to pass through the ferrule, a
threaded portion at the end of the shank opposite the head, and a
collar formed on the shank proximate the threaded portion. The
screw is captivated on the ferrule between the head and the collar.
The spring extends on the shank of the screw between the head and
the ferrule. Preferably, the ferrule has a generally cylindrical
exterior surface having a plurality of knurls for securing the
captive screw in a preformed aperture in a first structure, such as
a lever. It is also preferred that the ferrule be formed with an
inner ring formed on the interior surface of the ferrule having a
generally circular opening large enough to permit the threaded
portion and collar to pass through but not large enough to permit
the spring to pass through.
[0010] In a second embodiment of this invention, the ferrule has an
annular lip and an exterior circumferential exterior groove.
Preferably, the annular lip and exterior groove permit the captive
screw to be press fit in a structure.
[0011] In a third embodiment of the present invention, the ferrule
of the captive screw has a first and a second annular lip which
provide for the captive screw to be pressed into a structure.
[0012] In a fourth embodiment of the present invention, a captive
screw is provided which has a collar connected to the shank of the
screw in the proximity of the threaded portion of the screw. The
collar has outwardly extending legs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side elevational view of a first embodiment of a
captive screw according to the present invention, partially in
section in a heat sink and a circuit board.
[0014] FIG. 2 is an exploded perspective view of a first embodiment
of the screw of the captive screw of FIG. 1.
[0015] FIG. 3a is a side elevational cross-sectional view of the
captive screw of FIG. 1 in an unfastened position prior to
deformation.
[0016] FIG. 3b is a side elevational cross-sectional view of the
captive screw of FIG. 1 in an unfastened position post
deformation.
[0017] FIG. 4 is a side elevational cross-sectional view of the
captive screw of FIG. 1 in a fastened position post
deformation.
[0018] FIG. 5 is a side view of the captive screw of FIG. 1 in a
fastened position.
[0019] FIG. 6 is an isometric view of the captive screw of FIG. 1
in a fastened position.
[0020] FIG. 7 is a side view of the captive screw of FIG. 1 in an
unfastened position.
[0021] FIG. 8 is a perspective view of the captive screw of FIG. 1
in an unfastened position.
[0022] FIG. 9 is a top plan view of the captive screw of FIG.
1.
[0023] FIG. 10 is a side view of the screw in the captive screw of
FIG. 1.
[0024] FIG. 11 is a perspective view of the screw in the captive
screw of FIG. 1.
[0025] FIG. 12 is a perspective view of the spring in the captive
screw of FIG. 1.
[0026] FIG. 13 is a top view of the ferrule in the captive screw of
FIG. 1.
[0027] FIG. 14 is a side view of the ferrule in the captive screw
of FIG. 1.
[0028] FIG. 15 is a perspective view of the ferrule in the captive
screw of FIG. 1.
[0029] FIG. 16 is a side elevational view of a second embodiment of
the captive screw of the present invention partially in
section.
[0030] FIG. 17 is a side view of a third embodiment of the captive
screw of present invention.
[0031] FIG. 18 is a side elevational view of the captive screw of
FIG. 17 partially in section in a structure.
[0032] FIG. 19 is a side elevational view of a fourth embodiment of
a captive screw according to the present invention, partially in
section in a heat sink and a circuit board.
[0033] FIG. 20 is a side elevational view of the captive screw of
FIG. 19 partially in section in a structure.
[0034] FIG. 21 is a perspective view of the captive screw of FIG.
19.
[0035] FIG. 22 is a side elevational view of the captive screw of
FIG. 19.
[0036] FIG. 23 is a bottom view of the captive screw of FIG.
19.
[0037] FIG. 24 is a perspective view of the collar of the captive
screw of FIG. 19.
[0038] FIG. 25 is a perspective view of the collar of the captive
screw of FIG. 19.
DETAILED DESCRIPTION
[0039] The present invention provides a captive screw for securing
a first structure such as a first panel or heat sink to a second
structure such as a circuit board.
[0040] Referring now to the drawings in detail, wherein like
reference numerals indicate like elements throughout the several
views, there is shown in FIG. 1 a captive screw 10 according to the
present invention. The captive screw 10 includes a ferrule 20, a
screw 40 and a spring 50. The screw 40 (FIG. 2) includes a head 42
adapted to receive a driver (FIG. 3), a shank 44 adapted to pass
through the ferrule 20, and a threaded portion 46 at the end of the
shank 44 opposite the head 42. The screw 40 also includes a collar
48 formed on the shank 44 proximate the threaded portion 46.
[0041] The generally cylindrical ferrule 20 can have a plurality of
knurls formed on its exterior cylindrical surface for securing the
captive screw 10 in a preformed aperture 102 in a first structure
100 such as a heat sink by a press fit. The threaded portion 46 of
the screw 40 is intended for securing the captive screw 10 in a
preformed, threaded aperture 112 formed in second structure 110
such as a circuit board shown in FIG. 1 having a chip 5. The chip
is shown on a sheet 6 of flexible material which absorbs
vibrations. The captive screw 10 is positioned precisely relative
to the second structure by virtue of the collar 48 formed on the
shank 44 of the screw 40. The collar 48 limits the depth of
penetration of the screw 40 into a threaded insert 7 which has been
inserted from the bottom of the circuited board 112. Alternatively,
the threaded portion of the captive screw can be screwed directly
into a preformed, threaded aperture in a second structure. By
coming into contact with the threads of threaded insert 7, the
screw 40 is being rotationally driven into the second
structure.
[0042] As can be seen in FIGS, 1, 3a, 3b, and 4, the ferrule 20 is
formed with an annular ring section 24. The captive screw 10 is
assembled by placing the spring 50 on the screw 40 and then passing
the screw 40 through the ferrule 20. The annular ring 24 on the
interior surface of the ferrule is large enough to permit the
threads 46 of the screw 40 to pass through but not large enough to
permit the spring 50 to pass through. When the ferrule 20 is formed
during assembly, pressure can be applied uniformly on the generally
cylindrical portion of the ferrule and plastic deformation can form
the annular ring 24. Prior to the pressure being applied to the
ferrule, the ferrule can have an annular circumferential groove
which allows for the formation of the ring section. The annular
ring section 24 reduces the size of the opening in the ferrule so
that the resultant opening is slightly larger than the diameter of
the screw shaft 44 but smaller than both the screw head diameter
and the diameter of the collar 48, thus captivating the screw 40 on
the ferrule 20 in between the screw head 42 and the collar 48. The
collar 48 can be rolled onto the screw after the screw has been
inserted into the ferrule. Collar 48 has a tapered top surface and
a tapered bottom surface. After installation of the ferrule into
the first structure 100 the end of the ferrule can be flared. The
tapered top surface of the collar 48 mates with the tapered annular
ring 24 of the ferrule 20.
[0043] The ferrule 20 also has an annular lip 28 or stop formed on
the exterior cylindrical surface proximate the top of the ferrule
20 for limiting the penetration of the ferrule 20 in the preformed
aperture 102 in the first structure 100. When the captive screw 10
of the present invention is installed, the collar 48 precisely
limits the vertical position of the screw 40 above the second
structure 110, while the first structure 100 floats above the
second structure 110, while being urged towards the second
structure 110 by the spring 50 of the captive screw 10. For
example, FIG. 6 is a perspective view of the captive screw of the
first embodiment of the invention showing the position of the screw
when the screw is in a fastened position. FIG. 8 is a perspective
view of the captive screw of the first embodiment of the invention
showing the position of the screw when the screw is in an
unfastened position.
[0044] In the second embodiment of the invention as shown in FIG.
16, the ferrule 120 also has an annular lip 38 or stop formed on
the exterior cylindrical surface proximate the top of the ferrule
120 for limiting the penetration of the ferrule 120 in the
preformed aperture 102 in the first structure, as well as an
annular circumferential groove 30 formed in the exterior
cylindrical surface of the ferrule immediately adjacent and below
the annular lip 38, for receiving the plastic flow of material 104
when the ferrule 120 is pressed into the preformed aperture. When
the captive screw of 310 the present invention is installed, the
collar 48 precisely limits the vertical position of the screw 40
above the second structure (not shown), while the first structure
100 floats above the second structure, while being urged towards
the second structure by the spring 50 of the captive screw 310. The
captive screw shown in FIG. 1 can be pressed into the underside of
the first structure from the bottom. Alternately, the captive screw
shown could be installed from the top when groove 30 is placed near
the bottom of the first structure 30. Also, the collar of the
second embodiment can be shaped as part of the screw after the
screw has been inserted in the ferrule.
[0045] In the third embodiment of the invention as shown in FIGS.
17 and 18, the ferrule 220 also has a first annular lip 58 or stop
formed on the exterior cylindrical surface proximate the top of the
ferrule 220 for limiting the penetration of the ferrule 220 in the
preformed aperture 102 in the first structure, as well as an
annular circumferential groove 130 formed in the exterior
cylindrical surface of the ferrule immediately adjacent and below
the first annular lip 58, for receiving the plastic flow of
material 104 when the ferrule 220 is pressed into the preformed
aperture. A second annular lip 68 is shown at the opposite end of
the ferrule. When the captive screw of 210 the present invention is
installed, the collar 48 precisely limits the vertical position of
the screw 40 above the second structure (not shown), while the
first structure 100 floats above the second structure, while being
urged towards the second structure by the spring 50 of the captive
screw 210. In this embodiment of the present invention the collar
can be pressed on.
[0046] In the fourth embodiment, FIGS. 19, 20, 21 and 22 show a
captive screw in first structure 100 having a collar 148 which has
outwardly extending legs and a base portion. The collar has
outwardly extending legs 248 and the base portion 348. The ends 448
of the legs 248 extend outwardly and define a collar cross section.
Since the legs are flexible, the ends of the legs deform
elastically and permit the collar to pass through a first structure
when being passed through an aperture in a structure and the
aperture has a smaller cross section than that defined by the ends
of the legs. The arrangement shown in FIG. 19 is one way in which
to install the collar 48 into a second structure 110. The base
portion 348 of the collar limits the penetration of the screw into
the second structure. In the embodiment shown in FIG. 20 the ends
448 of the legs contact the underside of the first structure. The
collar can be in the shape of a crown and the collar can be
threaded on, crimped on or pressed on, etc. The legs are also
dimensioned and configured to not allow the spring to pass over the
legs.
[0047] The collar shown and described in the first three
embodiments can be rolled on pressed on or screwed on.
[0048] The screw in the above embodiments includes a generally
cylindrical head 42 having a central recess 34 formed therein and
adapted to receive a driver. While a Phillip-type driver recess is
illustrated, other types of driver recesses, such as slotted,
Torx.RTM., hexagonal, and the like, and combinations thereof (e.g.
slot-Torx), can also be used. A generally cylindrical upper section
extends coaxially downward from the head 42.
[0049] Preferably, the screw, and ferrule are formed from a
suitable metallic material such as aluminum.
[0050] While the ferrule of the present invention is adapted to be
press fit into the first structure, other means of mounting the
captive screw on the structure can be employed, including
conventional installation methods known as "flare-in," "floating,"
"p.c. board," and "snap-in" installation methods.
[0051] Various other modifications can be made in the details of
the various embodiments of the apparatus of the present invention,
all within the scope and spirit of the invention and defined by the
appended claims.
* * * * *