Mechanism for fixing a blood centrifuge bowl to a rotating spindle

A mechanism for fixing a blood centrifuge bowl to a rotating spindle is disclosed having two parts. The first part converts downward movement of an outer collar of a chuck into inward and downward pressure against a blood bowl to be secured in the chuck. The second part of the invention converts centrifugal forces present in a rotating chuck into downward pressure on the collar described above. In the preferred embodiment of the invention, the chuck comprises a base plate, plungers, a finger ring and a collar. The base plate receives and positions the blood bowl. The finger ring has a series of fingers located around its upper periphery that pivot around living hinges into contact with the blood bowl. The collar has an annular sloping finger contacting surface that contacts the outer surface of the fingers and forces them inward and downward into contact with the blood bowl. The base plate has a series of outwardly directed bores that hold plungers. Under rotation of the chuck, the plungers move outward in the bores under centrifugal force and contact a sloped plunger contacting surface on the inner surface of the collar. As the centrifugal force increases, the pressure exerted on the plunger contacting surface by the outer ends of the plungers increase causing the collar to be pressured to move downward. Downward pressure on the collar is translated into downward pressure on the finger contacting surface which in turn is translated into inward and downward pressure on the blood bowl.

BACKGROUND OF THE INVENTION 
FIELD OF THE INVENTION 
The invention relates to a device for attaching a bowl to a rotating 
spindle and more specifically relates to a device for fixing a blood 
centrifuge bowl to a rotating spindle. 
DESCRIPTION OF THE RELATED ART 
Blood processing systems and diagnostic hemostasis management systems for 
the operating room often use centrifuge devices to separate blood 
components. The separation of blood components is accomplished by 
introducing the blood into a blood bowl that is rapidly spun in a 
centrifuge device. 
Blood processing systems typically recover and wash red blood cells and 
separate and hold other beneficial blood components, such as platelets and 
plasma, for later reinfusion. Platelets and plasma may also be used to 
make "platelet gel," which can be applied to surgical wounds to reduce 
bleeding. 
One type of blood processing systems is an autologous blood transfusion 
device. Autologous blood transfusion devices rapidly collect, clean and 
separate the patient's own blood, known as autologous blood, into blood 
components and then reinfuse the desired blood components into the 
patient. Autologous blood transfusion reduces or eliminates a patient's 
dependence on blood donated by others, thereby reducing concerns about 
transmission of bloodborne diseases. One example of an autologous blood 
transfusion device is the Sequestra 1000 system sold by 
Medtronic-Electromedics in Parker, Colo. 
One approach to attaching a blood bowl to a rotating chuck has been to 
provide a chuck with radially, axially, inwardly moving dogs that move 
inwardly to grasp the blood bowl and thereby hold it in place. One problem 
with this approach is that a secondary tool is needed to actuate the 
inward and outward motion of the dogs. Another problem with this approach 
is that the dogs concentrate the clamp force at the dogs. Since there are 
relatively few dogs, there are relatively few clamp points. This results 
in increased stress on the blood bowl at each clamp point which is a 
potential cause of bowl failure. Examples of devices incorporating this 
type of chuck are the Model ELMD 500 and the Model AT 1000 cell-separating 
devices sold by Medtronic-Electromedics in Parker, Colo. 
Other designs for devices for holding blood bowls in a centrifuge device 
are known. One such device is shown in U.S. Pat. No. 5,851,169 entitled 
"ROTARY PLATE AND BOWL CLAMP FOR BLOOD CENTRIFUGE" which patent is 
commonly assigned with the present application. In this device, the chuck 
includes a ring that opens at one point to allow insertion of the blood 
bowl. The ring is then brought together contacting at least a portion of 
the blood bowl and securing the blood bowl within the chuck. 
One problem with this type of chuck is the large number of parts needed and 
the possibility of having an asymmetric chuck. An asymmetric chuck 
produces a moment of inertia for the chuck and blood bowl that is not 
aligned with the axis of rotation of the chuck and blood bowl. This 
misalignment of the axis of rotation and the moment of inertia causes 
unnatural stresses on the bearing controlling the rotation of the device. 
This misalignment may also cause a wobble in the rotation of the chuck and 
blood bowl. All of these undesirable characteristics of this type of 
system are preferably to be avoided. 
SUMMARY OF THE INVENTION 
A mechanism for fixing a blood centrifuge bowl to a rotating spindle is 
disclosed. In its broadest aspect, the invention has two parts. The first 
part converts downward movement of an outer collar of a chuck into inward 
and downward pressure against a blood bowl to be secured in the chuck. 
This inward and downward pressure secures the blood bowl in the chuck. The 
second part of the invention converts centrifugal forces present in a 
rotating chuck into downward pressure on the collar described above. This 
downward pressure on the collar is converted into inward and downward 
pressure against the blood bowl to be secured in the chuck. 
In the preferred embodiment of the invention, the chuck comprises a base 
plate, plungers, a finger ring and a collar. The base plate receives and 
positions the blood bowl. The finger ring has a series of fingers located 
around its upper periphery that pivot around living hinges. The collar has 
an annular sloping finger contacting surface that contacts the outer 
surface of the fingers. The annular sloping finger contacting surface 
slopes outwardly moving down the sloping surface so that downward movement 
of the collar causes inward pressure on the fingers. 
The collar also has an annular sloping plunger contacting surface that 
contacts the outer ends of the plungers. The annular sloping plunger 
contacting surface slopes inwardly moving down the sloping surface so that 
outer pressure on the plunger contacting surface causes downward pressure 
on the collar. 
The base plate preferably has a series of outwardly directed bores that 
hold plungers. Under rotation of the chuck, the plungers move outward in 
the bores under centrifugal force. The outer ends of the plungers contact 
the plunger contacting surface. As the centrifugal force increases, the 
pressure exerted on the plunger contacting surface by the outer ends of 
the plungers increase. The increasing pressure applied to the plunger 
contacting surface by the outer ends of the plungers causes the collar to 
be pressured to move downward. The downward pressure on the collar is 
translated into downward pressure on the finger contacting surface which 
in turn is translated into inward and downward direct pressure on the 
blood bowl. 
The many fingers of the present invention grip the blood bowl at many 
different locations around the circumference of the blood bowl. This 
spreads out and distributes the pressure exerted on the blood bowl by the 
fingers to a substantially the entire circumferential surface. By 
contrast, chucks having fewer bowl contacting pieces concentrate the 
gripping pressure over a few areas thereby producing increased pressure in 
these areas. As a result, in the present system, if a blood bowl has a 
geometric irregularity in or near the area of contact of the blood bowl, 
the pressure applied to the blood bowl in the area of the irregularity 
would be less than if there were fewer blood bowl contacting pieces. 
It is the primary object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle that is simple to manufacture 
and easy to use. 
It is a further object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle is inherently balanced. 
It is a further object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle that eliminates the need for 
dynamic balancing. 
It is another object of the present invention to provide a device for 
fixing a blood centrifuge bowl to a rotating spindle that eliminates the 
need for a secondary tool to actuate the chuck. 
It is another object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle that is self-locking during 
loading. 
It is another object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle that uses the centrifugal 
force present in a centrifuge operation to lock the blood centrifuge bowl 
to the rotating spindle. 
It is another object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle that has a low rotational 
inertia. 
It is a further object of the invention to provide a device for fixing a 
blood centrifuge bowl to a rotating spindle that accommodates 
irregularities in the blood bowl geometry. 
These and other objects of the invention will be clear from the following 
detailed description of the invention and in particular with reference to 
the attached drawings. In the attached drawings, like elements, wherever 
referred to, are referred as like reference numbers. 
Throughout this description, reference is made to "upper", "lower", "inner" 
and "outer" as well as to moving "upwardly", "downwardly", "inwardly" and 
"outwardly". "Upper" surfaces are those generally directed toward the 
label "A" in FIG. 1 while "lower" surfaces are those generally directed 
toward the label "B" in FIG. 1. "Inner" means generally being closer to 
central axis 32 while "outer" means generally being farther away from 
central axis 32. 
Movement "upward" or "upwardly" is movement generally toward "A" while 
movement "downward" or "downwardly" is movement generally toward "B". 
Movement "inward" or "inwardly" is movement generally toward central axis 
32. Movement "outward" or "outwardly" is movement generally away from 
central axis 32.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows the chuck for fixing a blood centrifuge bowl to a rotating 
spindle according to the present invention generally labeled 10. Chuck 10 
has four basic components: base plate 12, finger ring 14, collar 16 and 
plungers 18. 
The centrifugal blood bowl, generally labeled 20, contains the blood to be 
washed and separated into its components (FIG. 11). Blood bowl 20 is 
hollow and may be generally conical in shape. An example of blood bowl 20 
is the blood bowl sold in the Sequestra 1000 system sold by 
Medtronic-Electromedics in Parker, Colo. Blood bowl 20 preferably has a 
pilot 22 located on the central axis 24 of blood bowl 20. Pilot 22 extends 
away from the lower base 26 of blood bowl 20. Blood bowl 20 has an outer 
surface 28 and an outer edge 30 that is the outer-most edge of blood bowl 
20. 
Chuck 10 includes a generally disk shaped base plate 12 as shown in more 
detail in FIGS. 3 and 4. Base plate 12 has an upper surface 34 and 
preferably has a cylindrical pilot bore 36 that extends from upper surface 
34 of base plate 12. Pilot bore 36 is concentric with central axis 32 of 
base plate 12. Pilot bore 36 has an inner diameter slightly larger than 
the outer diameter of pilot 22. In this way, pilot bore 36 may receive 
pilot 22 when the central axis 24 of blood bowl 20 is aligned with central 
axis 32 of base plate 12 and blood bowl 20 is moved towards base plate 12. 
An annular ridge 38 extends upward from upper surface 34 around the outer 
periphery of base plate 12. The outer, upper corner of ridge 38 has a flat 
cam surface 40 formed at an angle to ridge 38. 
Base plate 12 has a series of plunger bores 42 formed in base plate 12 that 
extend radially from central axis 32. Preferably there are at least three 
plunger bores 42 to provide a balanced base plate 12 during 
centrifugation. However, it is to be understood that there may be more or 
fewer than three plunger bores 42. In the most preferred embodiment, there 
are six plunger bores 42. 
In the preferred embodiment shown in FIG. 4, plunger bores 42 extend within 
base plate 12 at an angle of about 10.degree. downward from the transverse 
axis 44 to central axis 32. In an alternate embodiment shown in FIG. 5A, 
plunger bores 42 extend through base plate 12 essentially parallel to 
transverse axis 44. Although these specific embodiments for plunger bores 
42 have been disclosed, plunger bores 42 at other angles, including angles 
upward from the transverse axis 44 are also within the scope of the 
invention. In addition, plunger bores 42 are not limited to being 
precisely aligned with radials from central axis 32. 
Each plunger bore 42 preferable has a spring 46 located at the end of 
plunger bore 42 closest to central axis 32. Spring 46 biases plunger 18 
within plunger bore 42 as will be described in detail hereafter. 
In the preferred embodiment, spring 46 performs the biasing function on 
plunger 18. In this preferred embodiment, the axes of compression of 
springs 46 and the corresponding axes of plunger bores 42 are aligned. 
However, it is anticipated that those skilled in the art will recognize 
means other than springs 46 for biasing plunger 18. Referring to FIG. 5B, 
examples of these biasing means 43 include but are not limited to magnetic 
repulsion, pneumatic pressure, hydraulic pressure, or, particularly in the 
embodiment of plunger bores 42 angled downward from the transverse axis 44 
to central axis 32, gravitational force. 
Base plate 12 also preferably has a series of lock actuator pin receiving 
slots 48 formed in ridge 38. Lock actuator pin receiving slots 48 extend 
downwardly into ridge 38 to receive lock actuator pins 50 as will be 
described in detail hereafter. Lock actuator pin receiving slots 48 extend 
downward into ridge 38 a sufficient distance to allow lock actuator pin 50 
to move downward sufficiently to allow blood bowl 20 to be securely 
positioned against base plate 12. 
Base plate 12 may be made of general plastics or ferrous or non-ferrous 
alloys including, but not limited to acetal, phenolics, polymide-imides, 
ABS, aluminum, titanium or tool steels by machining or molding as will be 
appreciated by those skilled in the art. However, it is to be understood 
that base plate 12 may also be made of any rigid, durable material. 
Chuck 10 includes a finger ring 14 as shown in more detail in FIGS. 6-8. 
Finger ring 14 has an annular base 52 with a series of fingers 54 
extending upward from base 52. Base 52 connects fingers 54 and provides a 
means for positioning fingers 54 by contacting ridge 38 as will be 
explained hereafter. In the preferred embodiment, there are 18 fingers 54 
although there may be more or fewer fingers 54 as desired. 
The cross-section view of finger ring 14 shown in FIG. 8 shows a single 
finger 54 in cross-section. Finger 54 has a collar contact surface 56, a 
bowl contact surface 58, a cam contact surface 60 and a living hinge 62. 
Living hinge 62 connects finger 54 to annular base 52 and allows finger 54 
to pivot around living hinge 62 relative to base 52. Fingers 54 are offset 
inwardly from base 52 at living hinge 62. As is best shown in FIGS. 6 and 
7, a space 64 separates each finger 54 from its neighboring finger 54 
around annular base 52. This allows fingers 54 to flex inwardly around 
each finger 54's respective living hinge 62 without contacting and 
interfering with adjoining fingers 54. 
Finger ring 14 is placed around ridge 38 as shown in FIGS. 1 and 2 so 
living hinges 62 allow fingers 54 to pivot toward and away from central 
axis 32 over ridge 38. In this configuration, base 52 is positioned around 
the periphery of ridge 38. Fingers 54 are prevented from moving too far 
inward over ridge 38 by contact between cam contact surface 60 and cam 
surface 40. 
Finger ring 14 is preferably made in one piece of a flexible polymeric 
material such as polyethylene, polypropylene, polyvinyl, acetyl or nylon. 
However, finger ring 14 may be made of any flexible, durable material. In 
addition, finger ring 14 may be made in several pieces and joined together 
as will be clear to those skilled in the art. 
A collar 16 is provided as shown in FIGS. 9 and 10. Collar 16 has a 
generally cylindrical main body 66 contoured to fit concentrically around 
finger ring 14 when finger ring 14 is in position around ridge 38 as 
described above. An annular finger contact surface 68 extends upwardly and 
inwardly from main body 66. Finger contact surface 68 is shaped to contact 
collar contact surface 56. The upper end of finger contact surface 68 
terminates in a generally upwardly directed upper collar surface 70. 
A plunger capture wall 72 is formed attached to and beneath main body 66 of 
collar 16. Generally, plunger capture wall 72 is formed a greater radial 
distance from central axis 32 than main body 66 to form a plunger capture 
space 74 defined by plunger capture wall 72. Plunger capture wall 72 has a 
substantially vertical upper wall 76 at a first distance from the central 
axis 32. Plunger capture wall 72 also has a substantially vertical lower 
wall 78 at a second distance from central axis 32. The second distance is 
less than the first distance. A build-up of material at the upper end of 
lower wall 78 forms an inwardly directed plunger resistance ridge 80. 
A sloping pressure wall 82 connects resistance ridge 80 to upper wall 76. 
Pressure wall 82 has an increasing inner diameter moving upward from 
resistance ridge 80 to upper wall 76. A plunger detent 84 connects 
resistance ridge 80 to lower wall 78. Plunger detent 84 is formed 
conformal to the outer end 86 of plunger 18. Plunger detent 84 conformally 
receives the outer end 86 of plunger 18 as will be explained hereafter. 
In the preferred embodiment, a lock actuator pin 50 extends inwardly from 
the main body 66 of collar 16. Lock actuator pin 50 has a length that 
allows lock actuator pin 50 to extend into and interact with lock actuator 
pin receiving slots 48 in base plate 12 when chuck 10 is assembled as will 
be explained hereafter. 
Collar 16 is preferably made of ferrous or non-ferrous alloys including, 
but not limited to, aluminum, titanium or tools steels by machining or 
other manufacturing means known to those skilled in the art. However, it 
is to be understood that collar 16 may also be made of any rigid, durable 
material. 
Collar 16 has been described as being generally cylindrical. This means 
that collar 16 has a generally tube shape with an inside and an outside 
surface. Collar 16 may also have a shape other than cylindrical including, 
but not limited to, conical so long as collar 16 has an inner surface and 
an outer surface as described herein. The inner surface of collar 16, in 
whatever shape collar 16 may be, should be configured to have a finger 
contact surface 68 or sloping pressure wall 82 or both. 
A plunger 18 is placed in each of the plunger bores 42. Plunger 18 
preferably has a cylindrical shape of slightly less outer diameter than 
the inner diameter of plunger bores 42. Plunger 18 has an inner end 90 and 
an outer end 86. Plungers 18 are also preferably made of a material having 
a relatively high density such as bronze, brass, copper, titanium tool 
steel, iron or babbit alloys, to name but a few possible choices. 
When in place within plunger bores 42, the inner end 90 of plunger 18 
contacts spring 46. Spring 46 biases the outer end 86 of plunger 18 
outwardly from central axis 32. Plunger 18 has a length that allows outer 
end 86 to extend a small distance out of plunger bore 42 when plunger 18 
is in plunger bore 42 and inner end 90 is in contact with spring 46. 
FIGS. 1 and 2 show the fully assembled chuck 10 in a locked and unlocked 
configuration, respectively. As can be seen, plungers 18 are placed in 
plunger bores 42 so that the inner ends 90 contact springs 46 and outer 
ends 86 extend a small distance out of plunger bores 42. Finger ring 14 is 
placed around base plate 12 so that base 52 encircles ridge 38. Base 52 is 
positioned along ridge 38 so that living hinge 62 allows cam contact 
surface 60 to pivot into and out of contact with cam surface 40. Collar 16 
is placed concentrically around both base plate 12 and finger ring 14 so 
that plungers 18 extend into plunger capture space 74. 
In the unlocked position shown in FIG. 2, collar 16 is moved upward so that 
plunger detent 84 receives the outer end 86 of plunger 18. In this 
position, plunger 18 slightly compresses spring 46 biasing the outer end 
86 of plunger 18 into firm contact with plunger detent 84. This firm 
pressure holds collar 16 is a raised position. In this raised position, 
finger contact surface 68 is raised upward from collar contact surface 56. 
As a result, finger contact surface 68 does not contact collar contact 
surface 56. This removes any inward pressure or bias against finger 54 and 
allows finger 54 to relax around living hinge 62. 
In this relaxed position, a blood bowl 20 can be moved downward into the 
chuck 10. Blood bowl 20 moves downwardly until pilot 22 locates itself in 
pilot bore 36. This is accomplished by aligning central axes 24 and 36 and 
moving blood bowl 20 downward into contact with base plate 12. As a 
result, blood bowl 20 contacts base plate 12 with central axis 24 and 
central axis 32 aligned and with pilot 22 engaged with pilot bore 36. As 
blood bowl 20 moves downwardly, the outer edge 30 of blood bowl 20 
contacts lock actuator pin 50. The contact of the outer edge 30 with lock 
actuator pin 50 moves the entire collar 16 downward with the downward 
movement of blood bowl 20. 
As blood bowl 20 and collar 16 move downward, finger contact surface 68 
moves into contact with collar contact surface 56. Finger contact surface 
68 has a decreasing inner diameter moving upward along finger contact 
surface 68. As a result, downward movement of finger contact surface 68 
causes inward and downward pressure on collar contact surface 56. This 
inward and downward pressure on collar contact surface 56 causes finger 54 
to pivot around living hinge 62. This inward and downward motion of finger 
54 around living hinge 62 causes bowl contact surface 58 to move into 
contact with the outer surface 28 of blood bowl 20. 
The more collar 16 moves downward, the more finger contact surface 68 moves 
fingers 54 inward and downward and in more secure contact with the outer 
surface 28 of blood bowl 20. This inward and downward pressure on blood 
bowl 20 causes blood bowl 20 to be securely seated against the pilot bore 
36 and ridge 38 of base plate 12. Contact between cam contacting surface 
60 and cam surface 40 prevents fingers 54 from moving too far inwardly or 
downwardly thereby exerting excessive pressure on outer surface 28 of 
blood bowl 20. 
Downward movement of collar 16 causes the outer end 86 of plungers 18 to 
move over resistance ridge 80 into contact with the sloped pressure wall 
82 of upper wall 76. When pilot 22 is securely located in pilot bore 36, 
the outer end 86 of plunger 18 contacts pressure wall 82 under the bias of 
spring 46 as shown in FIG. 1. 
In operation, chuck 10 is connected to a source of rotation so that chuck 
10 rotates around central axis 32 at high speed, typically around about 
5600 RPM. Operating at this rotational speed and with a typical outer 
diameter of chuck 10 of about six inches produces centrifugal forces on 
the outer surface of the chuck 10 in excess of 1400 times the force of 
gravity. This centrifugal force applies as well to plungers 18 within 
plunger bores 42. The centrifugal force applies an outwardly directed 
force on plungers 18 within bores 42. This outward force on plungers 18 
causes outer ends 86 to be biased against sloping pressure wall 82. As 
plungers 18 receive more centrifugal force, more outward force is applied 
against sloping pressure wall 82 by contact with outer end 86. 
Sloping pressure wall 82 slopes outwardly moving in an upward direction. As 
a result, increased outwardly directed pressure on outer end 86 against 
sloping pressure wall 82 causes sloping pressure wall 82 to be biased to 
move downwardly. As sloping pressure wall 82 tries to move downwardly, the 
entire collar 16 tries to move downwardly. As collar 16 tries to move 
downwardly, finger contact surface 68 tries to move downwardly. This 
downward pressure on finger contact surface 68 increases the pressure 
exerted against collar contact surface 56. The increased pressure against 
collar contact surface 56 creates greater inward and downward pressure by 
bowl contact surface 58 against the outer surface 28 of blood bowl 20. 
This increased inward and downward pressure by blood bowl contact surface 
58 on the outer surface 28 of blood bowl 20 holds bowl 20 firmly in 
position within chuck 10. 
To remove blood bowl 20 from chuck 10, collar 16 is pulled upward. This 
causes plungers 18 to move over resistance ridge 80 into plunger detent 
84. Simultaneously, finger contact surface 68 moves away from collar 
contact surface 56 allowing fingers 54 to relax around living hinge 62. 
This moves bowl contact surface 58 away from the outer surface 28 of blood 
bowl 20. Thereafter, blood bowl 20 is moved upward away from contact with 
base plate 12 and out of chuck 10. 
In the invention, downward pressure applied by collar 16, either by manual 
pressure or by the action of plungers 18, is transferred through fingers 
54 into inward and downward pressure on the outer surface 28 of blood bowl 
20. In the preferred embodiment, downward manual movement of blood bowl 20 
is transferred to collar 16 to cause downward movement and pressure on 
collar 16 through lock actuator pins 50. 
Although it is preferred to use lock actuator pins 50, an alternate 
embodiment of the invention does not include lock actuator pins 50. In 
this embodiment, blood bowl 20 is moved into contact with base plate 12 so 
that pilot 22 locates itself in pilot bore 36. Because there is no lock 
actuator pin 50, downward movement of blood bowl 20 does not cause 
downward movement of collar 16. Instead, once pilot 22 is secured in pilot 
bore 36, manual downward pressure is applied to the upper collar surface 
70. This moves collar 16 down so that finger contact surface 68 moves into 
contact with collar contact surface 56 and the outer end 86 of plunger 18 
moves over resistance ridge 62 into contact with the sloped pressure wall 
82 of upper wall 76. 
The preferred embodiment of the invention includes the combination a first 
part that converts downward movement of an outer collar of a chuck into 
inward and downward pressure against a blood bowl to be secured in the 
chuck and a second part that converts centrifugal forces present in a 
rotating chuck into downward pressure on the collar. The first part 
includes chuck 10 having collar 16 with finger contact surface 68, fingers 
54 with collar contact surface 56 and base plate 12. The second part 
includes chuck 10 having base plate 12 with plunger bores 42, collar 16 
with sloping pressure wall 82 and plungers 18. However, the first and 
second part may operate independently and exclusively of each other. 
Throughout this description, reference has been made to a preferred 
embodiment of centrifugal blood bowl 20. Blood bowl 20 has been described 
as having a pilot 22 located on the central axis 24 of blood bowl 20 that 
22 extends away from the lower base 26 of blood bowl 20. Blood bowl 20 
moves downwardly until pilot 22 locates itself in pilot bore 36. Although 
the preferred embodiment contemplates using a base plate 12 with a pilot 
bore 36, the invention in its broadest form does not require a blood bowl 
20 with a pilot 22 or a base plate 12 with a pilot bore 36. Instead, the 
invention requires that blood bowl 20 be securely in contact with base 
plate 12 in any configuration that will be clear to those skilled in the 
art. 
The invention has been described in connection with a specific embodiment. 
As described above, the specific embodiment includes a collar 16 having 
both a finger contact surface 68 and a sloping pressure wall 82. However, 
as described above, it is also within the scope of the invention to have a 
collar 16 having either a finger contact surface 68 or a sloping pressure 
wall 82, but not both. Further, it is to be understood that the 
description given herein is for the purpose of illustration only and is 
not intended to be limiting. Other changes and modifications will occur to 
those skilled in the art.