Abstract:
A pair of scissors has a first cutting blade with a thumb handle and a thumb ring and a second cutting blade with a finger ring. The second cutting blade is pivotally attached to the first cutting blade, and the first and second cutting blades pivot relative to one another within a first plane. The thumb ring is slidably attached to the first cutting blade by a shaft that moves freely but with a certain amount of friction along a longitudinal slot in the thumb handle of the first cutting blade when the scissors are in use. The longitudinal slot in the thumb handle is situated within a second plane that is perpendicular to the first plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority back to U.S. Patent Application No. 61/572,884 filed on Jul. 25, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of cutting shears, and more specifically, to cutting shears with a longitudinally slidable and preferably rotatable thumb ring that moves ergonomically with the thumb during use. 
     2. Description of the Related Art 
     There are a number of cutting shears incorporating longitudinally and/or rotationally adjustable thumb and finger rings that are the subject of issued patents or published patent applications, but none of these inventions includes the novel features of the present invention, most notably a thumb ring that is readily slidable back and forth in the longitudinal direction and readily pivotable for a comfortable thumb angle during use of the scissors, while in addition, the thumb ring is automatically restrained in its last position when the thumb is temporarily removed from the ring. 
     U.S. Pat. No. 1,479,908 (Goshia, 1924) discloses scissors with an automatically adjustable thumb ring that is connected to the shank of the scissors via a rivet pin fitted with a friction roller. The thumb ring is designed to slide forward and backward on the shank (i.e., the handle) with each opening and closing of the scissors. The thumb ring may be optionally locked in place with a set screw. There is no provision in this invention for automatic restraint of the ring when the thumb is removed from the ring. 
     U.S. Pat. No. 2,158,277 (Dolph, 1939) provides scissors with a manually adjustable thumb rive, which may be set to any one of a number of discreet positions along the shaft. The discreet positions are determined by a set of teeth along the shaft that mate with a set of matching teeth on the thumb ring. 
     U.S. Pat. No. 2,571,675 (Bray, 1951) describes scissors with removable thumb and finger rings, in which the thumb ring may be longitudinally adjusted and locked into position prior to use, and in which the diameters of the thumb and finger rings may be adjusted to fit hands of various sizes. 
     U.S. Pat. No. 4,642,895 (Gauvry, 1987) discloses scissors having a thumb loop that is rotatable longitudinally along and perpendicularly around the axis of the scissors handle by means of a ball and socket interconnection. The invention also comprises a rubber stop or bumper to limit the closing of the blades. In this invention, the thumb loop does not slide freely along the longitudinal axis of the handle; instead, it only rotates around the ball and socket joint. 
     U.S. Pat. No. 5,469,624 (Brenton et al., 1995) provides scissors and similar instruments that comprise interchangeable, rotatable and pivotable thumb and finger rings that incorporate a hand-adjustable tensioning means. The rings are not capable of sliding longitudinally alone the handle. 
     U.S. Pat. No. 6,212,780 (Huang, 2001) describes scissors and similar instruments that comprise a thumb ring that may be adjusted longitudinally alone the handle and set at discrete points prior to use, using a cam lock or screw as a locking means. 
     U.S. Pat. No. 6,249,977 (Knoop, 2001) discloses scissors having a T-shaped finger grip and a thumb ring grip, in which each of the two grips can be adjusted longitudinally along a handle and secured at the desired position with a locking screw. 
     U.S. Pat. No. 6,915,578 (Yusufov et al., 2005) and U.S. Patent Application Pub. No. 2004/0211068 (Yusufov et al., 2004) provide a reversible-blade scissors comprising finger and thumb rings that are longitudinally and pivotably adjustable. Each ring is secured both longitudinally and pivotably by a single thumb screw prior to use of the scissors. The shafts of the thumbs screws are fitted into longitudinal slots (i.e., tracks), in which the tracks are within flat sides of the handles, and the flat sides of the handles are in the same plane as the flat sides of the blades. 
     U.S. Pat. No. 7,424,778 (Brenton, 2008) and U.S. Patent Application Pub. No. 2005/0204569 (Brenton, 2005) describe scissors having a pivotably adjustable thumb ring, wherein the pivot shaft is made of flexible material, thereby allowing the ring to flex as well as pivot. There is no longitudinal adjustment of the thumb ring in this invention. 
     U.S. Pat. No. 7,966,733 (June, 2011) and U.S. Patent Application Pub. No. 2008/0172886 (June, 2008) disclose scissors comprising a thumb ring that is capable of rotating in two independent directions and pivoting around one axis that is parallel to the handle. The thumb ring of this invention is not capable of longitudinal adjustment. 
     U.S. Patent Application Pub. No. US 2006/0010695 (Wu, 2006) provides thumb and finger rings for scissors that are rotatable and detachable. There is no provision for longitudinal adjustment of the rings in this invention. 
     U.S. Patent Application Pub. No. US 2010/0192384 (Fox, 2010) describes shears having a pivotable and flexible finger ring. There is no provision for longitudinal adjustment of the ring in this invention: 
     U.S. Patent Application Pub. No. US 2010/0212165 (Parnazzina et al., 2010) discloses scissors with a pivotable thumb ring and saw-toothed edges on the blades. There is no provision for longitudinal thumb ring adjustment in this invention. 
     U.S. Patent Application Pub. No. US 2010/0242289 (Roskam et al., 2010) provides scissors comprising an articulated thumb ring that is magnetically attached to the handle. The thumb ring may be detached and reattached to the handle during use of the scissors without removing the ring from the thumb. 
     U.S. Patent Application Pub. No. US 2011/0016728 describes scissors with a thumb ring that is adjustable for offset, rotation, and diameter. There is no provision for longitudinal adjustment of the thumb ring in this invention. 
     U.S. Pat. Nos. D536,941 (Nenadich et al., 2007), D537,312 (Nenadich et al., 2007), and U.S. Design Pat. No. D538,612 (Nenadich et al., 2007) illustrate scissors having pivotable (but not longitudinally adjustable) thumb rings. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a pair of scissors comprising: a first cutting blade comprising a thumb handle and a thumb ring; a second cutting blade comprising a finger ring, wherein the second cutting blade is pivotally attached to the first cutting blade, and wherein the first and second cutting blades pivot relative to one another within a first plane that is defined by a first axis and a second axis; wherein the thumb ring is slidably attached to the first cutting blade by a shaft that moves freely but with a certain amount of friction along a longitudinal slot in the thumb handle of the first cutting blade when the scissors are in use; and wherein the longitudinal slot in the thumb handle is situated within a second plane that is defined by the first axis and a third axis that is perpendicular to the first and second axes so that the second plane is perpendicular to the first plane. 
     In a preferred embodiment, the invention further comprises a tensioning washer, a lower slide washer, and an upper slide washer; wherein the thumb handle comprises an upper surface and a lower surface; wherein the tensioning washer is situated between the thumb ring and the lower slide washer, the lower slide washer is situated between the tensioning washer and the lower surface of the thumb handle, and the upper slide washer is situated adjacent to the upper surface of the thumb handle directly above the longitudinal slot; wherein the shaft extends through the upper slide washer, the longitudinal slot in the thumb handle, the lower slide washer, and the tensioning washer; and wherein the shaft is connected to the thumb ring. 
     In an alternate embodiment, the invention further comprises a micro thrust bearing and an upper slide washer; wherein the thumb handle comprises an upper surface and a lower surface; wherein the micro thrust bearing is situated between the thumb ring and the lower surface of the thumb handle, and the upper slide washer is situated adjacent to the upper surface of the thumb handle directly above the longitudinal slot; wherein the shaft extends through the upper slide washer, the longitudinal slot in the thumb handle, and the micro thrust bearing; and wherein the shaft is connected to the thumb ring. 
     In yet another alternate embodiment, the invention further comprises a magnet, a lower slide washer and all upper slide washer; wherein the thumb handle comprises an upper surface and a lower surface; wherein the magnet is situated between the thumb ring and the lower slide washer, the lower slide washer is situated between the magnet and the lower surface of the thumb handle, and the upper slide washer is situated adjacent to the upper surface of the thumb handle directly above the longitudinal slot; wherein the shaft extends through the upper slide washer, the longitudinal slot in the thumb handle, the lower slide washer, and the magnet; and wherein the shaft is connected to the thumb ring. 
     In a preferred embodiment, the thumb ring rotates relative to the longitudinal slot. In an alternate embodiment, the shaft comprises a square portion that is configured to fit within the longitudinal slot in the thumb ring and that prevents the thumb ring from rotating relative to the longitudinal slot. In yet another alternate embodiment, the invention is a pair of scissors comprising: a first cutting blade comprising a thumb handle and a thumb ring; and a second cutting blade comprising a finger ring, wherein the second cutting blade is pivotally attached to the first cutting blade; wherein the thumb ring is slidably attached to the first cutting blade by a shaft that moves freely but with a certain amount of friction alone a longitudinal slot in the thumb handle of the first cutting blade when the scissors are in use; and wherein each of the first and second cutting blades comprises two flat sides, the thumb handle comprises two sliding surfaces, and the sliding surfaces of the thumb handle are perpendicular to the flat sides of the cutting blades. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the first embodiment of the present invention, showing a user&#39;s fingers inserted into the thumb and finger lines of the scissors. 
         FIG. 2  is a side view of the first embodiment of the present invention, in which the scissors bumper is installed rearward of the thumb ring. 
         FIG. 3  is a side view of an alternative embodiment of the present invention, in which the scissors bumper is installed forward of the thumb ring. 
         FIG. 4  is a side view of the first embodiment of the present invention including the thumb ring assembly and a portion of the thumb handle. 
         FIG. 5  is an exploded perspective view of the first embodiment of the present invention including the thumb ring assembly and a portion of the thumb handle. 
         FIG. 6  is a side view of the second embodiment of the present invention including the thumb ring assembly and a portion of the thumb handle. 
         FIG. 7  is an exploded perspective view of the second embodiment of the present invention including the thumb ring assembly and a portion of the thumb handle. 
         FIG. 8  is a side view of the third embodiment of the present invention including the thumb ring assembly and a portion of the thumb handle. 
         FIG. 9  is an exploded perspective view of the third embodiment of the present invention including the thumb ring assembly and a portion of the thumb handle. 
         FIG. 10  is a side view of an alternate embodiment of the present invention comprising a shaft with a square portion that allows the rotational orientation of the thumb ring  4  to be preset and locked prior to use. 
         FIG. 11  is an exploded perspective view of the embodiment shown in  FIG. 10 . 
         FIG. 12  is a side view of the first embodiment of the present invention that shows the thumb ring rotated approximately forty-five (45) degrees as compared to the view shown in  FIG. 4 . 
         FIG. 13  is a side view of the first embodiment of the present invention that comprises a thumb ring capable of rotating along two perpendicular axes. 
         FIG. 14  is a perspective view of the first embodiment of the present invention, illustrating the planar relationship between the cutting blades and thumb handle. 
     
    
    
     REFERENCE NUMBERS 
     
         
         
           
               1  Scissors 
               2  Thumb 
               3  Hand 
               4  Thumb ring 
               5  Thumb ring assembly, first embodiment 
               6  Third finger 
               7  Finger ring 
               8  First finger 
               9  Second finger 
               10  Finger handle 
               11  Adjustment slot 
               12  Thumb handle 
               13  Bumper 
               14  Lower standard washer 
               15  Tensioning washer 
               16  Lower slide washer 
               17  Upper slide washer 
               18  Upper standard washer 
               19  Screw 
               20  Arrow indicating longitudinal movement 
               21  Arrow indicating rotational movement 
               22  Thumb ring assembly, second embodiment 
               23  Micro thrust bearing 
               24  Thumb ring assembly, third embodiment 
               25  Thumb ring with integral threaded shaft 
               26  Integral threaded shaft 
               27  Spacer 
               28  Magnet 
               29  Nut 
               30  Thumb ring assembly, first embodiment (modified to incorporate threaded shaft) 
               31  Magnet with square center hole 
               32  Threaded shaft with square (non-threaded) center portion 
               33  Lower slide washer with square center hole 
               34  Upper slide washer with square center hole 
               35  Blades of scissors 
           
         
       
    
     DETAILED DESCRIPTION OF INVENTION 
     The present invention is cutting shears or scissors that incorporate a multiply adjustable thumb ring. As used herein, the terms “shears,” “cutting shears” and “scissors” are used interchangeably. Modes of adjustment of the thumb ring include adjustment of the longitudinal position of the thumb ring along the length of the handle and adjustment of the angular orientation of the thumb ring around an axis that is perpendicular to the long axis of the handle. Each mode of adjustment can be accomplished with the cutting hand without removing the thumb from the thumb ring or the finger from the finger ring. The ability to adjust the scissors as needed for a particular cutting operation and to adjust the scissors to fit the user&#39;s hand size and shape is important for reducing fatigue and for minimizing repetitive-motion injuries. 
     The ability to quickly and easily slide the thumb ring longitudinally along the sliding surfaces (i.e., the upper and lower surfaces) of the handle is particularly useful for cutting hair. For example, when the thumb ring is slid forward (toward the blades), the cutting strokes are more precise, which is useful for making delicate and high-precision cuts around the eyes and ears. Conversely, when the thumb ring is slid rearward, more force can be applied to the blades, which is useful for making fast cuts on non-critical areas, such as initial cropping of long hair. During haircutting, the hairdresser or barber typically switches from using scissors to using a comb multiple times; therefore, it is highly beneficial for the scissors thumb ring to remain in place when the thumb is temporarily removed from the ring for combing, etc. because the thumb can then re easily reinserted into the ring without minimal loss of time or energy. In a similar manner, it is beneficial for the rotational position of the thumb ring to remain fixed when the thumb is temporarily removed from the ring. The present invention is superior to the prior art because the adjustments of the thumb ring are easily and quickly made with the user&#39;s thumb and finger inserted into the rings of the scissors handles, and the adjustments maintain their positions until they are purposely readjusted. None of the inventions of the prior art has this capability. 
     The materials and design of the present invention are purposely optimized to provide low friction when longitudinal or rotational adjustments are desired, but they also provide adequate friction to hold the desired position of the thumb ring when movement is not desired. There are three major embodiments of the present invention. Different thumb ring assembly components are used in each of the three embodiments to provide controlled friction for the adjustable thumb ring. All of the embodiments comprise identical handles in which the sliding surfaces of the thumb handle are perpendicular to the flat sides of the scissors blades. Each thumb handle incorporates a longitudinal slot through which the thumb ring components are attached. The present invention may be used in combination with most types of conventional scissors by installing a slot in the thumb handle of the scissors. The slot provides a track for the moving components. The sliding surfaces of the thumb handle are highly polished to eliminate undesired friction. 
     In the first embodiment, the thumb ring is attached to the handle by a screw that passes through the handle slot. (As used in the claims, the term “shaft” is intended to encompass the shaft of a screw.) Several washers are mounted on the screw. These washers include low-friction slide washers installed on each side of the handle and in contact with the polished faces of the handle, one rubber tensioning washer and standard metal washers in contact with the thumb ring and the underside of the screw head. The slide washers are preferably made of polytetrafluoroethylene (PTFE; e.g., trade name TEFLON™), plastic or other slide-enhancing materials. The tensioning washer is preferably made of a compressible synthetic rubber such as neoprene or nitrile having a durometer hardness in the range of about 40 A to 80 A. The tensioning washer preferably has an uncompressed thickness of about 0.1 to 0.2 inch. During assembly, the screw is threaded into a threaded hole in the base of the thumb ring until the tensioning washer is compressed sufficiently to provide proper sliding and rotational friction for the thumb ring. 
     The second embodiment is similar to the first embodiment, except that the lower slide washer and tensioning washer of the first embodiment are replaced with a micro thrust bearing. The thrust bearing provides a very low-friction contact with the outside surface of the handle, while the required friction for the assembly is supplied by the slide washer in contact with the inside surface of the handle. The micro thrust bearing may be any suitable commercial product, such as part number 6655K12 from McMaster-Carr Supply Company of Aurora, Ohio. The latter part has steel ball bearings and an outside diameter of 0.5 inch, although the present invention is not limited to any particular outside diameter of the micro thrust bearing. The micro thrust bearing is preferably comprised of a ring in which ball bearings are embedded. The ring of the micro thrust bearing may be comprised of any suitable material, for example, plastic or nylon, and the ball bearings may be comprised of any suitable material, for example, steel or ceramic. 
     The third embodiment is similar to the first embodiment except that the tensioning washer is replaced by a cylindrical magnet. In this embodiment, friction between the outside slide washer and the contact surface of the handle is provided by a compression force resulting from the magnetic attraction between the magnet and the handle. For the third embodiment, the handle must be made of a metal material, such as stainless steel or chrome-plated carbon steel, that attracts magnets. Rare earth magnets, which have a strong magnetic field compared to iron magnets of the same size, are preferable for this invention because they are lighter and smaller than comparable-strength iron magnets. 
     It is possible to combine the features of two or more of the three embodiments to form a hybrid configuration. For example, the thumb ring assembly may comprise a micro thrust bearing (from the second embodiment) on one or both contact surfaces of the thumb handle in combination with a magnet (from the third embodiment) on one side of the handle. 
     The present invention preferably incorporates a polymer bumper mounted on the inner surface of one handle. This bumper contacts the inner surface of the opposing handle when the scissors are fully closed. The purpose of the bumper is to set the position of the blades relative to each other when the scissors are fully closed and to minimize wear that would otherwise occur if the hard inner surfaces of the handles came into direct contact during closing of the scissors. The bumper may optionally be placed either forward of the thumb ring (i.e., closer to the blades) or rearward of the thumb ring. Each of the embodiments of the present invention will operate correctly with either a forward-mounted or rearward-mounted bumper. 
     Each of the three embodiments comprises a threaded shaft that passes through the slot of the thumb handle and slides back and forth within the slot to provide longitudinal adjustment of the thumb ring. The threaded shaft may optionally be manufactured either as an integral piece of the ring component, or alternately, it may be a separate screw component or non-integral threaded shaft that threads into the ring component. The configuration of the threaded shaft (integral threaded shaft, non-integral threaded shaft or separate screw) does not affect the operation of the invention. 
     Each of the three embodiments may optionally comprise a threaded shaft with a square (non-threaded) center portion in lieu of a fully threaded shaft. The purpose of the square portion is to prevent rotational movement of the thumb ring. In this configuration, the angle of the thumb ring is preset and locked into position prior to use, while longitudinal movement is still permitted. The fixed rotational option may be preferred by some users. This embodiment is shown in  FIGS. 10 and 11 . As used herein, the term “square” is intended to also encompass rectangular. 
       FIG. 1  is a perspective view of scissors that incorporate the first embodiment of the present invention, shown with a user&#39;s fingers inserted into the thumb and finger rings of the scissors. Referring to  FIG. 1 , the scissors  1  are grasped so that the thumb  2  of the user&#39;s hand  3  is inserted into the thumb ring  4  of the first embodiment of the thumb ring assembly  5 , while the third finger  6  is inserted into the finger ring  7 , and the first finger  8  and second finger  9  are rested alone the outer surface of the finger handle  10 . Also shown in  FIG. 1  is the longitudinal adjustment slot  11  in thumb handle  12  and the scissors bumper  13 . As shown in the figure, the thumb ring assembly  5  is positioned at an intermediate position within the slot  11  (i.e., the thumb ring  5  assembly is rearward of the front edge of the slot  11 ). 
       FIG. 2  is a side view of the embodiment shown in  FIG. 1 , in which the scissors bumper  13  is installed rearward of the thumb ring assembly  5 .  FIG. 3  is a side view of an alternate embodiment of the present invention, in which the scissors bumper  13  is installed forward of the thumb ring assembly  5 . Note that in the embodiment shown in  FIG. 3 , the thumb ring may slide all the way to the rear of the longitudinal slot (not shown) with the scissors in a fully closed position.  FIGS. 2 and 3  illustrate that the present invention is equally compatible with scissors having either a rearward- or forward-mounted bumper. 
       FIG. 4  is a side view of the first embodiment of the present invention that shows the ring assembly  5  installed on the thumb handle  12 .  FIG. 5  is an exploded perspective view of the thumb ring assembly of the first embodiment. As shown in  FIGS. 4 and 5 , components of the thumb ring assembly  5  include the thumb ring  4 , lower standard washer  14 , tensioning washer  15 , lower slide washer  16 , upper slide washer  17 , upper standard washer  18 , and screw  19 . During assembly of the thumb ring assembly  5  to the thumb handle  12 , the screw  19  is passed through the adjustment slot  11  and then screwed into the threaded portion of the thumb ring  4 . The screw  19  is tightened until the tensioning washer  15  is partially compressed. The compression of the tensioning washer  15  produces friction between the lower slide washer  16  and the lower contacting surface of the thumb handle  12  and friction between the upper slide washer  17  and the upper contacting surface of the thumb handle  12 . 
     The compression of the tensioning washer  15  is increased by tightening the screw  19  until the resistance of the thumb ring  4  against rotational and longitudinal movement is at the correct level. The arrow  20  shown in  FIG. 5  indicates the direction of longitudinal movement of the thumb ring assembly  5 , and the arrow  21  indicates the direction of rotational movement of the thumb ring assembly  5  relative to the thumb handle  12 . As previously described, the correct level of friction is preferably low enough to allow the user to adjust the longitudinal and rotational position of the thumb ring  4  when the thumb  2  is positioned within the thumb ring  4 , while at the same time the friction level is great enough to cause the thumb ring  4  to stay in the set longitudinal and rotational positions when the thumb  2  is removed from the thumb ring  4 . 
     As shown in  FIG. 14 , the cutting shears pivot about an x and a y axis in a two-dimensional plane, whereas the longitudinal slot lies within a z axis that is perpendicular to the x and v axes. This orientation of the longitudinal slot is important to the present invention because it enables the shaft  19 ,  26 ,  31  to move more freely within the longitudinal slot than the slot of Yusufov, for example, which is oriented solely within the x-y plane. The shaft of Yusufov is not intended to move freely during use of the scissors. 
       FIG. 6  is a side view of the second embodiment of the present invention that shows the ring assembly (second embodiment)  22  installed on the thumb handle  12 .  FIG. 7  is an exploded perspective view of the thumb ring assembly  22  of the second embodiment. As shown in  FIGS. 6 and 7 , the thumb ring assembly  22  of the second embodiment comprises a thumb ring  4 , a lower standard washer  14 , a micro thrust bearing  23 , an upper slide washer  17 , an upper standard washer  18 , and a screw  19 . In the second embodiment, the components of the thumb ring assembly shown in  FIGS. 6 and 7  are connected to the thumb handle  12  by passing the screw  19  through the adjustment slot  11  and then tightening the screw  19  until the proper level of friction is achieved against longitudinal and rotational movement of the thumb ring  4 . 
       FIG. 8  is a side view of the third embodiment of the present invention that shows the ring assembly (third embodiment)  24  installed on the thumb handle  12 .  FIG. 9  is an exploded perspective view of the thumb ring assembly  24  of the third embodiment. As shown in  FIGS. 8 and 9 , the thumb ring assembly  24  of the third embodiment comprises a thumb ring  25  with integral threaded shaft  26 , a spacer  27 , a magnet  28 , a lower slide washer  16 , an upper slide washer  17 , and a nut  29 . In the third embodiment, the thumb ring assembly  24  is assembled to the thumb handle  12  by passing the integral threaded shaft  26  through the adjustment slot  11  and threading the nut  29  onto threaded shaft  26 . The tightening tension of the nut  29  is not critical in this embodiment because friction is supplied by the force of the magnet toward the thumb handle  12 , which pushes the lower slide washer  16  against the lower contact surface of the thumb handle  12 . The proper level of friction against longitudinal and rotational movement in this embodiment is set by adjusting the size of the magnet  28 . For example, installing a longer magnet, or a second identical magnet, will increase the friction of the thumb ring  25 . Although one or two magnets is/are preferred, the present invention is not limited to any particular number of magnets. 
     Although the first and second embodiments are shown with a screw  19 , and the third embodiment is shown with an integral threaded shaft  26 , any of the three embodiments could be made with a non-integral threaded shaft (similar to the partially threaded shaft  31  and nut  29  shown in  FIG. 11 ). 
       FIGS. 10 and 11  illustrate an optional feature that may be incorporated into any of the three embodiments previously described and is particularly shown here used with a modified form of the third embodiment.  FIG. 10  is a side view of the modified third embodiment of the present invention  30  that allows the rotational orientation of the thumb ring  4  to be preset and locked prior to use.  FIG. 11  is an exploded perspective view of the embodiment shown in  FIG. 10 . 
     As shown in  FIG. 11 , the modified thumb ring assembly of the third embodiment  30  is comprised of a thumb ring  4 , a spacer  27 , a magnet with a square central hole  31 , a threaded shaft with a central (non-threaded) square portion  32 , a lower slide washer with a square central hole  33 , an upper slide washer with a square central hole  34 , and a nut  29 . (Note that the magnet  31  could also be made with a round central hole if the central (non-threaded) square portion  32  of the threaded shaft were shorter.) The shaft  32  has threads on the lower end that thread into the thumb ring  4  and threads on the upper end that thread into the nut  29 . The square portion of the shaft  32  is sized so as to fit snuggly but moveably inside and against the sides of the slot  11 , thereby allowing the shaft  32  to slide longitudinally along, the length of the slot  11  but preventing it from rotating within the slot  11 . By this means, when the modified thumb ring assembly  30  is installed on the thumb handle  12 , the thumb ring assembly  30  is free to slide back and forth in the longitudinal direction as shown by the arrow  20  but is restrained from rotational movement. The shaft shown in  FIGS. 10 and 11  can be used with the tensioning washer of the first embodiment or the micro thrust bearing of the second embodiment, as long as these components have a square central hole. 
       FIG. 12  is a side view of the first embodiment of the present invention that shows the thumb ring rotated approximately forty-five (45) degrees as compared to the view shown in  FIG. 4 . The direction of rotational movement is indicated by the dashed arrow. The thumb ring is free to rotate during each opening, and closing of the scissors blades during use, thereby allowing the thumb orientation to constantly adjust to an optimal position for comfort and efficiency during each stroke of the scissors. 
       FIG. 13  is a side view of the first embodiment of the present invention that comprises a thumb ring capable of rotating along two perpendicular axes. The two axes of rotational movement are shown by the dashed arrows. Each direction of rotation is free to move during opening and closing of the blades during use. The dual-rotation thumb ring shown in  FIG. 13  is preferred over the single-rotation thumb ring shown in  FIG. 12  by some users and can be combined with any of the embodiments described herein. 
       FIG. 14  is a perspective view of the first embodiment of the present invention, illustrating relative orientation of the cutting blades and longitudinal slot on the thumb handle. Three-dimensional axes are also shown in the figure and are labeled x, y and z. Referring to  FIG. 14 , the flat sides of the blades  35  lie in a vertical plane (the x-y plane), and the flat side of the thumb handle  12  lies in the x-z plane. The x-z plane is perpendicular to the plane of the flat side of the blades  35 . These sliding surfaces are also perpendicular to the flat sides of the blades, as shown in the figure. By contrast, the sliding surfaces of Yusufov (U.S. Pat. No. 6,915,578) are in the same plane as the flat sides of the blades. By orienting the sliding surfaces so that they are perpendicular to the flat sides of the blades rather than in the same plane as the flat sides of the blades, the thumb ring  4  of the present invention can be more properly positioned to reduce strain on the user&#39;s thumb, thereby reducing fatigue and the risk of repetitive-motion injury. 
     Although the preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.