Captive nut

A captive nut having a knob, rotatable about a central longitudinal axis, the knob having an internally threaded longitudinal hole extending at least partially through the knob and a means to facilitate rotation of the knob. Also included is a hollow ferrule having a panel attachment means for attachment of the ferrule to a panel, and a knob captivation means wherein the knob is slidably and rotatably attached to an end of the ferrule such that when the nut is in a fully retracted position, the knob captivation means prevents the ferrule and the knob from separating.

BACKGROUND OF THE INVENTION 
This invention relates to a captive nut of a type used to attach a first 
panel containing one or more captive nuts to a second panel or frame 
having a like number of screws, threaded shafts, or the like, protruding 
from the second panel. In various situations, for example, in the fields 
of electronics or aviation, it is desirable to keep fasteners in position 
without loose items of hardware. Each captive nut is mounted on the first 
panel such that each nut stays attached to the first panel even when the 
nut threads are fully disengaged from the second panel containing a 
threaded shaft to which the upper panel is attached. 
The present invention is directed toward a captive nut which has a low 
profile, and may have various panel attachment means. These panel 
attachment means may include snap-in means (requiring no tools for 
installation), press-in means (for various panel materials including 
fiberglass, metals, and the like), flare-in means, and the like. When the 
captive nut is disengaged from the threaded shaft to which it has been 
attached, the upper knob section of the captive screw is biased upward 
such that the threads of the nut remain clear of the threads of the 
corresponding screw, threaded shaft, or the like. 
Prior to the present invention, there have been a variety of captive screws 
wherein a screw is captivated on an upper panel that mates with a threaded 
hole in a lower panel as shown, for example, in U.S. Pat. No. 5,382,124 to 
Frattarola. 
SUMMARY OF THE INVENTION 
This invention relates to a low profile, captive nut of a type for use when 
a first panel or other relatively thin, flat member is required to be 
mounted against a surface such as a that of a second panel or frame 
containing one or more screws, threaded shafts, or the like. Such screws, 
threaded shafts, or the like are mounted on the second panel or frame such 
that the longitudinal axis of each screw, threaded shaft or the like 
coincides with the axis of each captive nut used. 
In operation, typically the panels are brought together with the bottom 
surface of the upper panel flush with the top surface of the lower panel. 
Mounted upon the top surface of the upper panel are one or more captive 
nuts. The lower panel contains a like number of threaded rods, protruding 
screws, or the like in corresponding locations, such that when the two 
panels are brought together, each captive nut is attachable to a 
corresponding threaded rod, screw or the like. By rotating a knob portion 
containing an internally threaded hole of the same screw size as that of 
the threaded rod, the upper and lower panels may be attached together. 
However, when separated, the captive nut remains attached to the upper 
panel so that the nuts will not be lost or misplaced. 
In one preferred embodiment, the captive nut comprises a knob and a 
ferrule. The knob is rotatable about a central longitudinal axis, having 
an internally threaded longitudinal hole extending at least partially 
through the central longitudinal axis of the knob, and a means to 
facilitate rotation. The ferrule is substantially hollow and has a panel 
attachment means for attachment of the ferrule to a panel. The captive nut 
also has a knob captivation means such that the ferrule is slidably and 
rotatably attached to the knob. When the nut is in a fully retracted 
position, the knob captivation means prevents the ferrule and the knob 
from separating.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now in detail to the drawings, wherein like reference numerals 
indicate like elements throughout the several views, there is shown in 
FIGS. 1 through 4 a captive nut 10 in accordance with one preferred 
embodiment of the present invention. The illustrative device is shown 
generally comprising a generally cylindrical, partially hollow knob 20, a 
generally cylindrical, hollow ferrule 30, a spring 40 or other biasing 
means, and a knob captivation means 50. The knob captivation means 50 
provides for slidable and rotatable attachment of the knob 20 to the 
ferrule 30 such that, when the captive nut 10 is in a fully retracted 
position, the knob captivation means 50 prevents the ferrule 30 and the 
knob 20 from separating. 
The generally cylindrical knob 20 has a substantially solid upper knob 
portion 22 and a substantially hollow lower knob 24 portion. The knob 20 
is rotatable about its central axis A. As can be seen in FIGS. 1 and 3, an 
internally threaded hole 26 extends partially through the solid portion 22 
of the knob 20 through the central axis A. Alternatively, a threaded hole 
26' can extend fully through knob 20. Having hole 26' extend through knob 
20 provides for a large range of screw or threaded rod lengths that can be 
accommodated when using the captive nut 10. This threaded hole 26 or 26' 
provides the "nut" for attachment to a threaded rod, screw, or the like 
70. 
The substantially hollow lower knob portion 24 of the knob 20 provides for 
axial movement of the knob 20 which contains the internally threaded hole 
26 or 26', such that the nut can be threaded down onto a threaded rod, 
screw or the like 70. The inside diameter of the hollow lower knob portion 
24 is larger than the outside diameter of the main body 34 of the ferrule 
30 as can be seen in FIGS. 1 and 2. The knob 20 thus has the ability to 
axially slide over the ferrule such that axial movement, generally equal 
in length to the axial length of the hollow lower knob portion 24 of the 
knob 20, is available. 
In FIG. 1, an upper, first panel 80 is shown with a captive nut attached. 
FIG. 1 also shows a lower, second panel 82 containing a rigidly mounted 
threaded rod 70. This figure shows one example of two panels 80, 82 prior 
to attachment. FIG. 2 shows the two panels as attached. Note that, in FIG. 
2, the knob 20 has traveled downward along axis A such that one end of the 
ferrule 30 is now in contact with a surface of the solid portion 22 of the 
knob 20. 
Optionally disposed on the outer circumference of the knob 20 are axially 
scored lines 34 to facilitate tightening of the nut 10 using only fingers 
without any tools, or to facilitate the initial alignment of the screw 
threads 26 with a threaded hole in the lower panel. Alternate embodiments 
may include a knurling pattern or other frictional surface. For example, 
FIGS. 11, 11a and FIGS. 16 and 16a depict captive nuts having a smooth 
knob, but with a recess for a slotted screwdriver. The captive nut of 
FIGS. 11 and 11a have a separate, pressed-in insert 90 (depicted in FIG. 
14) that is internally threaded on one end and has the recess on the 
opposing end. Advantageously here, the knob 20 may be constructed of a 
different material than that of the insert 90. For example, the outer knob 
20 may be aluminum, while the insert 90 may be steel such that the 
advantages of light weight, plus strong internal threads and screw head 
recess are provided. Likewise, FIGS. 12 and 12a, and FIGS. 13 and 13a 
depict similar designs using an insert 90, however, with an alternate hex 
insert and Phillips insert respectively. Alternatively, as shown in FIGS. 
15 and 15a and 16 and 16a, a screw driver recess may be made be part of 
the knob 20 material itself. FIGS. 17 and 17a further depict a hex shaped 
knob 20', such that a standard wrench may be used. 
The ferrule 30 has a first end 32 containing the panel attachment means 60, 
a main body 34, and a second end 36 containing a portion of the knob 
captivation means 50. As described above, the knob 20 is rotatably 
attached to the ferrule 30, however, full rotational movement of the knob 
with respect to the ferrule 30, and a limited amount of axial movement of 
the knob 20 with respect to the ferrule 30, corresponding approximately to 
the axial length of the hollow portion of the knob 20 combined with the 
axial length of the ferrule 30 are provided. 
The axial movement of the knob 20 is limited by the knob captivation means 
50 and by the axial length of the ferrule combined with the hollow portion 
of the knob 20 as described above and depicted in FIGS. 1 and 2. The knob 
captivation means 50 includes a first annular flange 21 on the knob 
extending inward from the inner surface 25 of the hollow knob 20 towards 
the central axis A of the knob 20, in combination with a second annular 
flange 37, integral to the ferrule 30, extending generally radially 
outward from the body of the ferrule 30 at the knob end or second end of 
the ferrule 30. The inside surface of the hollow portion 24 of the knob 20 
has a larger diameter than the outside diameter of the main body 34 of the 
ferrule 30 such that a portion of the ferrule 30 is slidable within the 
hollow cylindrical body of the knob 20. As can be seen in FIG. 2, when the 
captive nut 10 is engaged, i.e. when two panels are rigidly connected by 
the captive nut 10, the second end of the ferrule 30 is fully inserted 
into the hollow cylindrical body of the knob 30. The first and second 
annular flanges 21 and 37 allow the knob 20 and the ferrule 30 to be a 
single non-detachable assembly, while allowing for axial movement of the 
knob 20 with respect to the ferrule 30. 
At the end of the ferrule opposite the knob captivation means 50 is a panel 
attachment means 60. Such a panel attachment means 60 can be any known in 
the art, such as the press-in configuration 60 generally used for metals 
such as aluminum, steel, or the like as shown in FIGS. 1 and 2, the 
press-in configuration 60' generally used for fiberglass, printed circuit 
boards, or the like as shown in FIGS. 5 and 6, the floating panel 
configuration 60" as shown in FIG. 7 for use when greater tolerances are 
desired for locating the nut on the panel, the snap-in configuration 60'" 
as shown in FIGS. 8 and 9 (see U.S. Pat. No. 5,382,124) and the flare-in 
configuration 60"" as shown in FIG. 10. 
Optionally, encased between the ferrule 30 and the knob 20 is spring 40. 
Ferrule 30 preferably has a two stage internal diameter: a lower internal 
diameter 31 and an upper internal diameter 33. The lower internal diameter 
31 allows clearance for threaded shaft 70 while the upper internal 
diameter 33 has an internal diameter large enough to accommodate the 
threaded shaft 70 with spring 40 surrounding it. The annular ledge 35 
created with the two different internal diameters 31 and 33 serves to 
function as a termination point for one end of spring 40. The opposite end 
of spring 40 is terminated at the under side 28 of the solid portion 22 of 
knob 20. When the spring 40 is in its most uncompressed position, the knob 
20 is at its most retracted position, i.e. the annular flanges 21 and 37 
are in contact with each other. Here, the knob 20 is fully retracted. The 
spring 40 provides for retraction of the knob 20, and thus the threaded 
hole 26 or nut portion of the knob away from top surface of the panel 80 
to which the captive nut 10 is attached. Thus, advantageously, it can 
easily be seen whether a captive nut is secured or not secured when a 
first panel 80 is attached to a second panel 82 by observing the height of 
the knob 20 of the captive nut 10. Additionally, the travel of the knob 20 
relative to the ferrule 30 allows for the two panels 80, 82 to be placed 
flush against one another prior to the clamping down of the nut 10, 
assuming the proper length threaded rod or screw 70 is selected. 
It will be recognized by those skilled in the art that changes may be made 
in the above described embodiments of the invention without departing from 
the broad inventive concepts thereof. It is understood, therefore, that 
this invention is not limited to the particular embodiments disclosed, but 
is intended to cover all modifications which are within the scope and 
spirit of the invention as defined by the appended claims.