Abstract:
A self-aligning plunger rod and a non-elastomeric plastic plunger insert assembly for use with an elastomeric plunger in a cartridge or syringe barrel for manual or power-assisted withdrawing of fluid from a site or expelling fluid from the cartridge or syringe barrel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a self-aligning plunger rod for use in a syringe or cartridge barrel having a plunger and containing a parenteral solution therein, or in a syringe or cartridge which are empty and are to be filled with a parenteral solution by the user at the time of administration. 
     The present invention also relates to a plunger rod for use in a syringe or cartridge containing a parenteral solution therein intended to be dispensed from a power injector. 
     2. Reported Developments 
     Syringes and cartridges made of glass or polymeric materials for dispensing parenteral solutions or withdrawing biological fluids from a patient are well known in the prior art. They comprise a cylindrical barrel with a tapered portion at one end to which a needle or luer connector can be attached, and an open end which is stoppered by a plunger of a resilient thermoplastic or elastomeric material. The plunger serves the function of a stopper, when the barrel is filled with a fluid, or as a slidable member to expel the fluid from the barrel or withdraw a biological fluid from a patient or another source. 
     In order to expel fluid from the barrel or withdraw fluid into the barrel, the plunger is moved toward the distal end or the proximal end of the barrel by a plunger rod which is attachable to the plunger typically by screw threads. The user exerts a force, manually or by the use of a power injector, on the plunger rod to push or pull the plunger in the barrel. While the plunger rod does not contact the fluid in the barrel, it serves a very important function: it causes the plunger to move in an axial direction back and forth in the barrel when an external force is applied thereon. 
     The force applied to the plunger by the plunger rod should be perpendicular to the plunger so that the force exerted on the wall of the barrel by the plunger is uniform around the 360° of its cylindrical configuration. When the plunger rod flexes in the barrel, the direction of force on the plunger will not be uniform resulting in pressure points at certain areas of contact between the plunger and the inside wall of the barrel and, conversely, inadequate pressure points at other parts of the interface between the plunger and the inside wall of the barrel. Such pressure differences tend to allow leakage and difficulty in moving the plunger at an even rate in the barrel. 
     Typical prior art devices have fixed connections between plunger rods and plungers; they are either one-piece combinations of plunger rods and plungers or two-piece combinations wherein the plunger rods are threaded into the plungers. Some plungers are equipped with rigid plastic inserts having internal threads therein in order to support the elastomeric plunger heads and to engage the plunger rods and hold them in an axial orientation. Both approaches allow some movement of the plunger rods in a lateral direction which may result in leakage of the medical fluid from the syringe barrel. 
     Recognizing the importance of dimensional stability, the prior art has incorporated various stability enhancing means into plunger rods which include the following. 
     The assembly disclosed in U.S. Pat. No. 4,543,093 has a plunger rod, the central portion of which is almost as large as the inside diameter of the syringe barrel so that it will assist in keeping the plunger rod assembly concentrically aligned within the syringe barrel. 
     WO 93/09827 discloses a shank having a plurality of longitudinal and radially extending vanes. In one preferred embodiment the shank is provided with four vanes in an “X” pattern, while in another preferred embodiment, the shank is provided with three vanes forming a “Y” pattern. 
     U.S. Pat. Nos. 5,700,247 and 5,860,961 disclose plunger rods having a plurality of vanes or support ribs. 
     A common feature of these plunger rods is a shank extending between the distal and proximal ends of the plunger rods having vanes or support ribs thereon. The vanes or support ribs are identical with one another running longitudinally on the shank and extending radially therefrom. This feature is an improvement over typical plunger rods in that the plunger rods have limited flexibility in the lateral direction, thereby exerting pressure on the plunger surface in an axial direction. However, we have found that even limited flexibility of the plunger rods allow lateral movement of the plungers in syringe barrels. This lateral movement of the plunger rods attached to plungers can cause leakage of fluid from the syringe barrels. 
     An object of the present invention is to provide a plunger rod and plastic plunger insert combination which directs the force exerted on the plunger rod in an axial direction. The elastomeric plunger placed on the plastic plunger insert will exert a uniform force on the inside wall of the syringe barrel thereby preventing leakage of the fluid content from the syringe barrel. 
     Another object of the present invention is to provide a reinforced plunger rod in combination with a plastic plunger insert which may be used either manually or in a power injector. Reinforced plunger rods without plastic plunger inserts are disclosed in co-pending application Ser. No. 09/273,901 filed on Mar. 22, 1999 which is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided a plunger rod and plastic plunger insert combination having a self-aligning feature wherein the plunger rod tip fits into the socket of the plunger insert and freely glides therein. This feature allows the plunger rod tip to float in the socket of the plastic plunger insert and eliminates lateral pressure on the plastic plunger insert. The plastic plunger insert is equipped with an elastomeric plunger which may be of various configurations. 
     The self-aligning plunge rod and plastic plunger insert combination comprises: 
     a) a plunger rod having a distal end and a proximal end comprising: 
     longitudinal radially extending vanes; 
     a thumb rest at the proximal end; 
     a disc at the distal end; and 
     a plunger rod tip extending from the disc at the distal end designed to engage a plastic plunger insert, said plunger rod tip comprising a neck portion and a ball portion, the ball portion having slots therein extending axially from the neck portion; 
     b) a non-elastomeric plastic plunger insert comprising: 
     a cylindrical shaft having a distal end and a proximal end; 
     a cone-shaped head extending from the distal end of the cylindrical shaft having an inside surface and an outside surface; 
     a cavity in the cone-shaped head defined by a cylindrical rim and the inside surface of the cone-shaped head; 
     a plurality of tabs extending from the cylindrical rim into the cavity; and 
     a plurality of notches or openings between the tabs designed to receive the slotted ball portion of the plunger rod tip. 
     In use, the slots of the plunger rod tip are aligned with the notches or openings in the plastic insert. The ball portion of the plunger rod tip is inserted into the cavity of the plastic insert and rotated to engage the tabs of the plastic insert. 
     In a second embodiment of the present invention a reinforced plunger rod body is used in combination with the plunger rod tip and the plastic insert. The reinforced plunger rod body having a distal end and a proximal end comprises: 
     an end disc at the distal end; 
     a plunger rod tip extending from the end disc designed to engage a plastic plunger insert, said plunger rod tip comprising a neck portion and a ball portion, the ball portion having slots therein extending axially from the neck portion; 
     a thumb rest at the proximal end for facilitating exertion of external pressure on the plunger rod; 
     a reinforcing disc at about the longitudinal mid-point of the plunger rod; 
     a first pair of rectangular radially extending vanes connecting the end disc and the reinforcing disc; 
     a second pair of rectangular radially extending vanes connecting the reinforcing disc and the thumb rest; 
     a first pair of isosceles triangular radially extending vanes connecting the end disc and the reinforcing disc, wherein the smallest angle of the isosceles triangular vanes point toward the reinforcing disc; and 
     a second pair of isosceles triangular radially extending vanes connecting the reinforcing disc and the thumb rest, wherein the smallest angle of the isosceles triangular vanes point toward the reinforcing disc, wherein: 
     said first pair of said rectangular radially extending vanes and said first pair of said isosceles triangular radially extending vanes are integral with each other and with said end disc and said reinforcing disc; and 
     said second pair of said rectangular radially extending vanes and said second pair of said isosceles triangular radially extending vanes are integral with each other and with said reinforcing disc and said thumb rest. 
     In a third embodiment of the present invention, a reinforced plunger rod body of a different configuration from that of the reinforced plunger rod body of the second embodiment is used in combination with the plunger rod tip and the plastic insert. 
     The reinforced plunger rod having a distal end and a proximal end comprises: 
     an end disc at the distal end; 
     a plunger rod tip extending from the end disc designed to engage a plastic plunger insert, said plunger rod tip comprising a neck portion and a ball portion, the ball portion having slots therein extending axially from the neck portion; 
     a thumb rest at the proximal end for facilitating exertion of external pressure on the plunger rod; 
     a reinforcing disc at about the longitudinal mid-point of the plunger rod; 
     a first pair of rectangular radially extending vanes connecting the end disc and the reinforcing disc; 
     a second pair of rectangular radially extending vanes connecting the reinforcing disc and the thumb rest; 
     a first pair of isosceles triangular radially extending vanes connecting the end disc and the reinforcing disc, wherein the smallest angle of the isosceles triangular vanes point toward the reinforcing disc; and 
     a second pair of isosceles triangular radially extending vanes connecting the reinforcing disc and the thumb rest, wherein the smallest angle of the isosceles triangular vanes point toward the reinforcing disc, wherein: 
     said first pair of said rectangular radially extending vanes and said first pair of said isosceles triangular radially extending vanes are integral with each other and with said end disc and said reinforcing disc; and 
     said second pair of said rectangular radially extending vanes and said second pair of said isosceles triangular radially extending vanes are integral with each other and with said reinforcing disc and said thumb rest. 
     In use, the slots of the plunger rod tip are aligned with the notches or openings in the plastic insert. The ball portion of the plunger rod tip is inserted into the cavity of the plastic insert and rotated to engage the tabs of the plastic insert. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a prospective view of a prior art plunger rod; 
     FIG. 2 is a side elevational view thereof; 
     FIG. 3 is a bottom plan view thereof; 
     FIG. 4 is a top plan view thereof; 
     FIG. 5 is a perspective view of the plunger rod of the present invention; 
     FIG. 6 is a cross-sectional view thereof taken along the line  6 — 6  of FIG. 5; 
     FIG. 7 is a bottom plan view thereof; 
     FIG. 8 is a top plan view thereof; 
     FIG. 9 is a top plan view of a plastic insert of the present invention which is to engage the plunger rod; 
     FIG. 10 is a cross-sectional view of the plastic insert taken along the line  10 — 10  of FIG. 9; 
     FIG. 11 is a bottom plan view of the plastic insert; 
     FIG. 12 shows in a partial cross-sectional view of the assembly of the plunger rod and the plastic insert; 
     FIG. 13 is a perspective view of one embodiment of the present invention showing a reinforced plunger rod; 
     FIG. 13A is a cross-sectional view of the reinforced plunger rod taken along the line  13 A— 13 A of FIG. 13; 
     FIG. 13B is another cross-sectional view of the reinforced plunger rod taken along the line  13 B— 13 B of FIG. 13; 
     FIG. 14 is a side-elevational view of the reinforced plunger rod shown in FIG. 13; 
     FIG. 15 is another side-elevational view of the reinforced plunger rod shown in FIG. 13 rotated 90° from that shown in FIG. 14; 
     FIG. 16 is a bottom plan view of the reinforced plunger rod shown in FIG. 13; 
     FIG. 17 is the top plan view of the reinforced plunger rod shown in FIG. 13; 
     FIG. 18 is a perspective view of another embodiment of the present invention showing a reinforced plunger rod; 
     FIG. 18A is a cross-sectional view of the reinforced plunger rod taken along the line  18 A— 18 A of FIG. 18; 
     FIG. 18B is a cross-sectional view of the reinforced plunger rod taken along the line  18 B— 18 B of FIG. 18; 
     FIG. 19 is a side-elevational view of the reinforced plunger rod shown in FIG. 18; 
     FIG. 20 is another side-elevational view of the reinforced plunger rod shown in FIG. 18 rotated 90° from that shown in FIG. 19; 
     FIG. 21 is a bottom plan view of the reinforced plunger rod shown in FIG. 18; and 
     FIG. 22 is a top plan view of the reinforced plunger rod shown in FIG.  18 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawings, like numerals with ′ or ″ denote the same parts of the device in different embodiments of the present invention. 
     Referring to FIGS. 1-4, a typical prior art plunger rod is shown in perspective, side elevational, bottom plan, and top plan views. Plunger rod  1  having a distal end  2  and a proximal end  3  comprises: longitudinal and radially extending vanes  4   a ,  4   b ,  4   c  and  4   d  ( 4   d  is hidden in the perspective view); a thumb rest  5  at the proximal end and a disc  6  at the distal end  2  of the plunger rod; and a screw threaded member  7  extending from disc  6  designed to engage a plunger. Vanes  4   a ,  4   b ,  4   c  and  4   d  are equivalent to one another extending from thumb rest  5  to disc  6 . These vanes meeting at the center  8  of the plunger rod are of rectangular configuration. 
     The plunger rod is threaded into an elastomeric plunger which also contains thread means for engagement with the plunger rod. When the plunger rod joined with the plunger is inserted into the barrel of a syringe or cartridge to expel medical fluid contained in the barrel, the manual force exerted on the plunger rod will move the plunger towards the distal end of the barrel. However, this manual force has two components: a large force in the axial direction; and a smaller force in the lateral direction. This smaller force tends to cause non-uniform pressure points at certain areas of contact between the plunger and the inside wall of the barrel. Such pressure differences tend to allow leakage of the content of the barrel and creates difficulty in moving the plunger at an even rate in the barrel. 
     We have now discovered a plunger rod and plastic plunger insert combination having a self-aligning feature wherein the plunger rod tip fits into the socket of the plunger insert and freely glides therein. This feature allows the plunger rod tip to float in the socket of the plastic plunger insert and eliminates lateral pressure on the plastic plunger insert. This and other advantageous features will be explained in the description of the invention in reference to the drawings. 
     Referring to FIGS. 5-8, showing perspective, side elevational, bottom and top plan views, there is shown a plunger rod  8  (generally designated) having a distal end  10  and a proximal end  12  comprising: longitudinal radially extending vanes  14   a ,  14   b ,  14   c  and  14   d  ( 14   d  is hidden); a thumb rest  16  at the proximal end, and a disc  18  at the distal end; and plunger rod tip  20  (generally designated) extending from disc  18  designed to engage a plastic insert. Plunger rod tip  20  is integral with disc  18  and comprises: a neck portion  22  and a ball portion  24 , the ball portion having slots  24   a ,  24   b ,  24   c  and  24   d  therein extending axially from the neck portion. 
     The self-aligning plunger rod  8  of the present invention is used in combination with a plastic insert, the top plan view of which is shown in FIG.  9 . It is of a generally cone-shaped configuration best seen in FIG. 10 which is a cross-sectional view of the plastic insert, taken along the line  10 — 10  of FIG.  9 . The plastic insert, generally designated by the numeral  26 , comprises: a cylindrical shaft  28  having a distal end  30 , and a proximal end  32 ; between the distal and proximal ends there is provided a cylindrical recess or groove  34 ; a cone-shaped head  36  extending from distal end  30  and terminating in zenith  38 ; and a cylindrical flange  40  extending from the proximal end  32 . 
     FIG. 11 shows a bottom plan view of the plastic insert  26  which comprises: a first cylindrical rim  42  constituting the underside of cylindrical flange  40 ; a second cylindrical rim  44  adjacent to said first cylindrical rim and projecting slightly above the horizontal surface of the first cylindrical rim; a plurality of reinforcing rods  46  connecting the first cylindrical rim  42  and the second cylindrical rim  44 ; a cavity  48  defined within said second cylindrical rim and the inside surface of the cone-shaped head  36 ; and a plurality of tabs  50  extending from the second cylindrical rim  44  into cavity  48 . Between tabs  50  there are notches  52  to receive the slotted ball portion of the plunger rod tip. 
     FIG. 11 shows:  8  reinforcing rods, however, less than 8 or more than 8 rods may be used; 4 tabs are shown, however, two or three tabs or more than four tabs may be used. Similarly, four slots are shown in FIG. 8 of the ball portion of the plunger rod tip. However, more or less slots may be used as long as the number of slots in the ball portion match the number of tabs in the plastic insert  26 . 
     FIG. 12 shows in a partial cross-sectional view the assembly of the self-aligning plunger rod  8  and the plastic insert combination  26 . The ball portion  24  of the plunger rod tip  20  fits into the cavity or socket  48  of the cone-shaped head  36  and freely moves therein, essentially floating within the cavity or socket. Any external pressure on the plunger rod is directed in an axial direction and does not impact the integrity of the seal formed by an elastomeric plunger head cover (not shown) and the inside wall of a syringe or cartridge barrel (not shown). 
     As illustrated in FIG. 12, plastic insert  26  is adapted to receive various elastomeric plunger head covers (not shown) by virtue of the design of the plastic insert  26  having a cylindrical recess  34  to hold an oppositely configured elastomeric plunger head. In addition, cylindrical grooves  52  are designed to receive and hold different configurational elastomeric plunger head covers with slight protuberances therein to fit into the grooves  52  of the cone-shaped head  36  of the plastic insert  26 . 
     In use, slots  24   a ,  24   b ,  24   c  and  24   d  of plunger rod tip  20  are aligned with cylindrical openings  54  in the plastic insert  26 . The ball portion  24  of the plunger rod tip is inserted into the cavity  48  of the plastic insert. When inserted, the plunger rod is rotated {fraction (1/4+L )} turn and is held by tabs  50 . To remove the plunger rod from the cavity of the plastic insert, the plunger rod is turned {fraction (1/4+L )} turn forward or backward. 
     FIGS. 13-17 show an embodiment of the present invention having a reinforced plunger rod used in combination with the plunger tip and plastic insert above-described, wherein: 
     FIG. 13 is a perspective view of the reinforced plunger rod; 
     FIG. 13A is a cross-sectional view of the reinforced plunger rod taken along the line  13 A— 13 A of FIG. 13; 
     FIG. 13B is another cross-sectional view of the reinforced plunger rod taken along the line  13 B— 13 B of FIG. 13; 
     FIG. 14 is a side-elevational view of the reinforced plunger rod shown in FIG. 13; 
     FIG. 15 is another side-elevational view of the reinforced plunger rod shown in FIG. 13 rotated 90° from that shown in FIG. 14; 
     FIG. 16 is a bottom plan view of the reinforced plunger rod shown in FIG. 13; and 
     FIG. 17 is the top plan view of the reinforced plunger rod shown in FIG.  13 . 
     Self-aligning reinforced plunger rod  60 , having a distal end  62  and a proximal end  64  comprises: 
     longitudinally extending radial vanes  66   a  and  66   b  having a rectangular configuration; 
     longitudinally extending radial vanes  70   a  and  70   b  having a triangular configuration; 
     a thumb rest  72  at the proximal end; 
     a disc  74  at the distal end; 
     a central disc  76  located at about the mid point between thumb rest  72  and disc  74 ; and 
     a plunger rod tip  20 ′ (generally designated) extending form disc  74  designed to engage a plastic insert. 
     Plunger rod tip  20 ′ is integral with disc  74  and comprises: a neck portion  22 ′, and a ball portion  24 ′, the ball portion having slots  24   a ′,  24   b ′,  24   c ′ and  24   d ′ therein extending axially from the neck portion. 
     The reinforced plunger rod  60  is used in combination with plastic insert  26  which is shown and described in FIGS. 9-12. 
     FIGS. 18-22 show another embodiment of the present invention having a reinforced plunger rod used in combination with the plunger tip and plastic insert above-described, wherein: 
     FIG. 18 is a perspective view of the reinforced plunger rod; 
     FIG. 18A is a cross-sectional view of the reinforced plunger rod taken along the line  18 A— 18 A of FIG. 18; 
     FIG. 18B is a cross-sectional view of the reinforced plunger rod taken along the line  18 B— 18 B of FIG. 18; 
     FIG. 19 is a side-elevational view of the reinforced plunger rod shown in FIG. 18; 
     FIG. 20 is another side-elevational view of the reinforced plunger rod shown in FIG. 18 rotated 90° from that shown in FIG. 19; 
     FIG. 21 is a bottom plan view of the reinforced plunger rod shown in FIG. 18; and 
     FIG. 22 is a top plan view of the reinforced plunger rod shown in FIG.  18 . 
     Plunger rod  80  having a distal end  82  and a proximal end  84  comprises: 
     longitudinal radially extending vanes  86   a ,  86   b , ( 86   c  and  86   d  are hidden in FIG. 18) having a rectangular configuration; 
     longitudinal radially extending vanes  88   a ,  88   b ,  88   c  and  88   d  having triangular configuration; 
     thumb rest  90  at the proximal end  84  of the plunger rod  80 ; 
     a disc  92  at the distal end  82  of the plunger rod; 
     plunger rod tip  94  extending from disc  92  designed to engage a plastic insert; and 
     a central disc  96  located at about the mid point between thumb rest  90  and disc  92 . 
     Central disc  96  supports the rectangular vanes and the triangular vanes and is integral therewith to provide dimensional stability to the plunger rod. Cross sectional view FIG. 18A taken along the line  18 A— 18 A of FIG. 18 illustrates that at about the mid point of the plunger rod the rectangular and triangular vanes are about equal in size in the radial direction, however, while the rectangular vanes connecting to the central disc  96 , disc  92  and thumb rest  90  maintain their rectangular configuration, the triangular vanes diminish in size in the radial direction as they approach disc  92  and thumb rest  90 . As shown, the triangular vanes merge with the rectangular vanes at disc  92  and thumb rest  90 . Cross-sectional view of the plunger rod in FIG. 18B, taken along the line  18 B— 18 B of FIG. 18 shows that triangular vanes  88   a ,  88   b ,  88   c  and  88   d  diminish to a small size and merge with rectangular vanes  86   a  and  86   b  at disc  92  and thumb rest  90 . 
     FIG. 19 shows the plunger rod of FIG. 18 in a side-elevational view where triangular vanes  88   a  and  88   b  are at the center of the Fig., and rectangular vanes  86   a ,  86   b ,  86   c  and  86   d  are at the sides of the Fig. 
     FIG. 20 is another side-elevational view of the plunger rod of FIG. 18 rotated 90° from that shown in FIG.  19 . The triangular vanes  88   a ,  88   b ,  88   c  and  88   d  are at the sides of the Fig. and rectangular vanes  86   a  and  86   d  are at the center thereof. 
     FIGS. 21 and 22 show respectively the bottom and top plan views of the plunger rod. 
     Plunger rod tip  20 ″ is integral with disc  92  and comprises: 
     a neck portion  22 ″, and a ball portion  24 ″, the ball portion having slots  24   a ″,  24   b ″,  24   c ″ and  24   d ″ therein extending axially from the neck portion. 
     The reinforced plunger rod  80  is used in combination with plastic insert  26  which is shown and described in FIGS. 9-12. 
     The plunger rods and the plastic insert assemblies of the present invention are made by injection molding, well-known in the art, using thermoplastic materials. Polypropylene, polyethylene and blends thereof are preferred for providing strength to the plunger rods. However, other polymers, such as polystyrenes, polyesters and polycarbonates may also be used. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE NUMBERS USED 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 PRIOR ART 
                   
               
               
                 Plunger rod 
                 1 
               
               
                 Distal end of plunger rod 
                 2 
               
               
                 Proximal end of plunger rod 
                 3 
               
               
                 Vanes of plunger rod 
                 4a, 4b, 4c &amp; 4d 
               
               
                 Thimb rest 
                 5 
               
               
                 Disc 
                 6 
               
               
                 Screw threaded member 
                 7 
               
               
                 PRESENT INVENTION (FORST EMBODIMENT) 
               
               
                 Self-aligning plunger rod (generally designated) 
                 8 
               
               
                 Distal end of self-aligning pluger rod 
                 10 
               
               
                 Proximal end of self-aligning plunger rod 
                 12 
               
               
                 Longitudinal, radially extending vanes 
                 14a, 14b, 14c &amp; 14d 
               
               
                 Thumb rest at the proximal end 
                 16 
               
               
                 Disc at distal end 
                 18 
               
               
                 Plunger rod tip (generally designated) 
                 20 
               
               
                 Neck portion of plunger rod tip 
                 22 
               
               
                 Ball portion of plunger rod tip 
                 24 
               
               
                 Slots in ball portion 
                 24a, 24b, 24c &amp; 24d 
               
               
                 Plastic insert (generally designated) 
                 26 
               
               
                 Cylindrical shaft of plastic insert (generally 
                 28 
               
               
                 designated) 
               
               
                 Distal end of cylindrical shaft 
                 30 
               
               
                 Proximal end of cylindrical shaft 
                 32 
               
               
                 Cylindrical recess or groove in cylindrical shaft 
                 34 
               
               
                 Cone-shaped head 
                 36 
               
               
                 Zenith of cone-shaped head 
                 38 
               
               
                 Cylindrical flange of cylindrical shaft 
                 40 
               
               
                 First cylindrical rim on the underside of flange 40 
                 42 
               
               
                 Second cylindrical rim 
                 44 
               
               
                 Plurality of reinforcing rods 
                 46 
               
               
                 Cavity inside of the cone-shaped head 
                 48 
               
               
                 Plurality of tabs extending into cavity 48 
                 50 
               
               
                 Cylindrical notches in the outside surface of the ball 
                 52 
               
               
                 portion of plastic insert 
               
               
                 Cylindrical openings in the inside surface of plastic 
                 54 
               
               
                 insert 
               
               
                 PRESENT INVENTION (SECOND 
               
               
                 EMBODIMENT) 
               
               
                 Self-aligning plunger rod (generally designated) 
                 60 
               
               
                 Distal end of self-aligning plunger rod 
                 62 
               
               
                 Proximal end of self-aligning plunger rod 
                 64 
               
               
                 Longitudinal, radially extending vanes having a 
                 66a, 66b, 66c &amp; 66d 
               
               
                 rectangular configuration 
               
               
                 Longitudinal, radially extending vanes having a 
                 68a, 68b, 68c, 68d, 
               
               
                 triangular configuration 
                 70a &amp; 70b 
               
               
                 Thumb rest 
                 72 
               
               
                 Disc at the distal end of plunger rod 
                 74 
               
               
                 Central disc 
                 76 
               
               
                 Plunger rod tip (generally designated) 
                 20′ 
               
               
                 Neck portion of plunger rod tip 
                 22′ 
               
               
                 Ball portion of plunger rod tip 
                 24′ 
               
               
                 Slots in ball portion 
                 24a′, 24b′, 24c′ &amp; 
               
               
                   
                 24d′ 
               
               
                 PRESENT INVENTION (THIRD 
               
               
                 EMBODIMENT) 
               
               
                 Plunger rod 
                 80 
               
               
                 Distal end of plunger rod 
                 82 
               
               
                 Proximal end of plunger rod 
                 84 
               
               
                 Longitudinal radially extending vanes having a 
                 86a, 86b, 86c &amp; 86d 
               
               
                 rectangular configuration 
               
               
                 Longitudinal radially extending vanes having a 
                 88a, 88b, 88c &amp; 88d 
               
               
                 triangular configuration 
               
               
                 Thumb rest 
                 90 
               
               
                 Disc at distal end 
                 92 
               
               
                 Central disc 
                 96 
               
               
                 Plunger rod tip (generally designated) 
                 20″ 
               
               
                 Neck portion of plunger rod tip 
                 22″ 
               
               
                 Ball portion of plunger rod tip 
                 24″ 
               
               
                 Slots in ball portion 
                 24a″, 24b″, 24c″ &amp; 
               
               
                   
                 24d″ 
               
               
                   
               
             
          
         
       
     
     Various modifications of the present invention will become apparent to those skilled in the art. This invention is intended to include such modifications to be limited only by the scope of the claims.