Abstract:
A driver bit and a header punch for manufacture of screws comprising a screw comprising substantially vertical end wall portions of predetermined depth formed on an end edge portion of a bit fitting groove on a screw head, non-planar bottom portions raised from lower edge portions of the vertical end wall portions toward a center of the screw head, inclined groove portions extending from raised portions of the non-planar bottom portions toward a center of a screw neck, a substantially conical-shaped bottom surface formed on a bottom of the groove, the bit fitting groove being adapted to a driver bit, which has a blade adapted to be fitted into the bit fitting groove and has a lower edge portion of the blade adapted to abut against the non-planar bottom portions. In this manner, groove portions of a cross groove on the screw are improved in construction, whereby it is possible to effectively prevent a driver bit from coming out, prevent breakage of screws caused in the prior art, always achieve an appropriate and rapid screw fastening work even when the cross groove of the screw is broken, and to significantly enhance an efficiency in work.

Description:
This is a continuation of application Ser. No. 09/284,881, filed Apr. 22, 1991, now U.S. Pat. No. 6,341,546, which is a National Stage Application of PCT/JP97/02237 Jun. 27, 1997, both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to a screw and a driver bit used for the screw. Especially, the present invention relates to a screw having a bit fitting groove that is suitable for both a Phillips® screwdriver and a flat blade screwdriver, and a driver bit used for the screw. More specifically, the present invention relates to a screw having a cross groove formed on the top thereof and a driver bit suitable for the screw, which can engage tightly each other so as to realize quick and secure fastening and loosening by constant and appropriate torque transmission, as well as a header punch for manufacture of screws. 
     B. Description of the Related Art 
     Conventionally, a general combination of a screw and a driver bit having a configuration shown in FIGS. 29-32 is known. FIGS. 29 and 30 show a conventional screw having a cross groove, FIG. 31 shows a driver bit for the screw having a cross groove, and FIG. 32 shows a state in which the screw and the driver bit are engaged with each other. 
     The conventional screw  10  shown in FIG. 29 has a cross groove  12  on the screw head  10   a . This cross groove  12  has inclined groove portions  12   a  extending from the edge portion to the center of the neck portion  12   b  and a bottom portion with a substantially conical-shaped bottom surface  14  as a gentle slope. Reference numeral  13  denotes tapered wall portions formed between neighboring cross grooves  12 . This tapered wall portions  13  abut and engage a blade of a driver bit mentioned below. On a corner portion neighboring each of the inclined groove portions  12   a , a tapered connection surface  17   a  or  17   b  is formed respectively, which extends from the position of the conical-shaped bottom surface  14  to the opening rim portion of the cross groove  12  at the screw head  10   a . These tapered connection surfaces  17   a  and  17   b  are also adapted to engage a part of the blade of a driver bit mentioned below. 
     On the other hand, the conventional driver bit  20  shown in FIG. 31 has blades  22  for engaging the cross groove  12  of the screw  10  and extension blade  22   a  adapted to the contour of the inclined groove portions  12   a  extending from the end edge portion of the cross groove  12  toward the center of the screw neck  12   b . The reference numeral  23  denotes tapered walls formed on both side surfaces of the blade  22  and the extension blade  22   a . This tapered wall  23  abuts and engages the tapered wall portions  13  formed on the cross groove  12  of the screw  10 . 
     The conventional combination of the screw and the driver bit having above-mentioned configuration, as shown in FIG. 32, when the screw  10  engages the driver bit  20 , the blades  22  and extension blades  22   a  of the driver bit  20  fit in the inclined groove portions  12   a  of the cross groove  12 , and the side walls  23  of the blades  22  and extension blades  22   a  abut the tapered walls  13  of the cross groove  12  of the screw  10 . Thus, a desired torque is transmitted to the screw  10  by rotating the driver bit  20 . Namely, the screw can be fastened to or loosened from an object. 
     In addition, a plus-and-minus screw (i.e., a screw with a cross grooved and slotted head)  10  having a configuration shown in FIGS. 33 and 34 is known, for example, as a screw having a fitting groove that can be fit both a Phillips® screwdriver bit and a flat-blade screwdriver bit. As a screwdriver bit that is used for the plus-and-minus screw  10 , the Phillips® screwdriver bit  20  having the configuration shown in FIG. 31 is used. FIG. 35 shows a state in which the plus-and-minus screw  10  and the Phillips® screwdriver bit  20  engage each other. 
     The plus-and-minus screw  10  has an advantage in that a conventional flat-blade screwdriver can also be used. 
     Therefore, the conventional plus-and-minus screw  10  shown in FIG. 33 and 34 has a cross groove, i.e., a fitting groove  12  on the screw head  10   a . This fitting groove  12  consists of a pair of linear grooves  12   a  and  12   b  crossing in the center of the screw head  10   a . One linear groove  12   a  is adapted to abut and engage the blade of a Phillips® screwdriver, and the other groove  12   b  is adapted to abut and engage the blade of a flat-blade screwdriver. 
     The linear groove  12   a  includes an inclined groove portions  12   a  extending from the edge rime portion to the center portion of the screw neck  10   b  and the substantially conical-shaped bottom surface  14  formed as a gentle slope at the bottom. Both sides of the inclined groove portions  12   a  is provided with tapered walls  13   a  having a taper toward the bottom. This tapered wall  13   a  abuts and engages the blade of the Phillips® screwdriver bit as explained below. 
     In addition, the other linear groove  12   b  is formed as a horizontal groove ( 12   a ) that has a sufficient width and depth for abutting and engaging the blade of the flat-blade screwdriver bit. Both sides of the horizontal groove  12   a  is provided with vertical walls  13   b  that extend substantially vertically toward the bottom. This vertical wall  13   b  abuts and engages the blade of the conventional flat-blade screwdriver bit. 
     The corner portions between the linear groove (the inclined groove)  12   a  and the other linear groove (the horizontal groove)  12   b  neighboring thereof are provided with tapered connection surfaces  17   a  and  17   b . A part of the blade of the drive bit mentioned below also abut and engage the tapered connection surfaces  17   a  and  17   b.    
     Therefore, the conventional Phillips® screwdriver bit  20  shown in FIG. 31 has a blade  22  that engages the fitting groove  12  of the plus-and-minus screw  10  and am extension blade  22   a  extending so as to fit the contour of the inclined groove portions  12   a  extending from the edge portion of the fitting groove  12  to the center portion of the screw neck  10   b . The reference numeral  23  denotes the tapered wall portions formed at both side surfaces of the blade  22  and extension blade  22   a . Namely, this tapered wall portion  23  abuts and engages the tapered wall  13   a  formed on one of the inclined groove portions  12   a  of the fitting groove  12  of the plus-and-minus screw  10 . 
     According to the combination of the conventional plus-and-minus screw and the Phillips® screwdriver bit, as shown in FIG. 35, when the plus-and-minus screw  10  and the Phillips® screwdriver bit  20  are engaged with each other, the blades  22  and the extension blade  22   a  of the Phillips® screwdriver bit  20  fit in the fitting groove  12  as mentioned above. One of the pair of the blade  22  and the tapered wall  23  of the extension blade  22   a  abuts the tapered wall  13   a  formed on one of the inclined groove portions  12   a  of the plus-and-minus screw  10 . Thus, when the Phillips® screwdriver bit  20  is rotated, a desired torque is transmitted to the plus-and-minus screw  10 . Namely, the plus-and-minus screw  10  can be fastened to or loosened from an object. 
     However, according to the combination of the conventional screw (the plus-and-minus screw)  10  and the driver bit (the Phillips® screwdriver bit)  20 , as shown in FIG. 32 (FIG.  35 ), the cross groove  12  of the screw head  10   a  has an inclined groove portions  12   a  extending from the edge portion to the center of the screw neck  10   b . On the other hand, the corresponding driver bit  20  is adapted so that the edge line portion of the extension blade  22   a  fit to the contour of the inclined groove portions  12   a  to engage the cross groove (the fitting groove)  12 . In addition, the width of the edge line portion of the extension blade  22   a  increases little by little from the front to the rear. 
     Furthermore, since the tapered wall  23  formed on each blade  22  of the driver bit  20  also abuts and engages the tapered wall  13  formed on the cross groove  12  (the inclined groove portions  12   a ) of the screw (the plus-and-minus screw)  10 , when the driver bit  20  is rotated in a predetermined direction, the contact state of the driver bit  20  with the cross groove  12  (inclined groove portions  12   a ) is such as a tapered contact in the entire surface. Therefore, the tip of the driver bit  20  has a tendency to come out along the slant surface of the inclined groove portions  12   a  of the cross groove  12  (as shown with an arrow in FIG.  32 ). This phenomenon is called a come-out phenomenon. 
     Especially, the contour of the cross groove (the fitting groove) of the conventional screw, as shown in FIG. 30 (FIG.  34 ), has the width of the cross groove (the fitting groove)  12  that is relatively larger than the width of the edge line portion of the extension blade  22   a  of the driver bit  20 , for example, in order to make easy engagement of the blade tip of the driver bit  20 , while the area of tapered wall  13  (and the vertical wall  13   b  ) and the tapered connection surface  17   a ,  17   b  that are formed on the boundary portion between the neighboring cross grooves  12 ,  12  (between the linear grooves  12   a  and  12   b  crossing each other) or on the corners is relatively small. Therefore, when rotating the driver bit  20 , the tapered wall  13  (and the vertical wall  13   b  ) and the tapered connection surface  17   a ,  17   b  are loaded with much stress, and the tapered wall  13 (and the vertical wall  13   b ) and the tapered connection surface  17   a ,  17   b  will be broken little by little as shown by the hatching portion  15  in FIG. 30 (FIG.  34 ), if the fastening resistance is large. If the breakage portion ( 15 ) is enlarged, the come-out phenomenon of the driver bit  20  occurs frequently, and finally fastening operation becomes impossible. 
     From the above-mentioned view point, a strong pressure of the driver bit  20  against the screw groove portion  12   a  is necessary to prevent the come-out phenomenon of the driver bit  20  when rotating the driver bit  20 . However, if the object to which the screw is fastened is such as a fine component, the object can be broken or damaged, while there is no problem if the object has a high stiffness like a metal. 
     In addition, if the come-out phenomenon occurs, abrasion of the tip portion of the bit, i.e., the blade  22  and the extension blade  22   a  is accelerated, and the abrasion causes more occurrence of the come-out phenomenon and further breakage of the screw groove. 
     Furthermore, if the excessive force is added to the driver bit  20  to prevent the come-out phenomenon, it becomes difficult to transmit a correct torque to the screw. Namely, the force added to the driver bit  20  my varies depending on an operator. As a result, the fastening torque of the screw may vary. 
     Still furthermore, if the screw is a tapping screw, a propulsion friction is added to a rotation friction of the screw when the screw is fastened to an object such as a plastic. Therefore, the object is heated so that the hardness of the fastening portion of the object may be lowered, or the object to which the screw is fastened may be broken. 
     On the other hand, the operation of rotating and pressing the driver bit  20  simultaneously is a difficult and tiresome job for the operator when fastening the screw. 
     In addition, according to the combination of the conventional screw  10  and the driver bit  20 , it is difficult to maintain the state where the axis of the screw is coaxial with the axis of the driver bit when fitting the tip of the bit with the screw groove while performing the rotation of the screw when using a manual or electric tool for fastening the screw. If the axis of the driver bit is inclined from the axis of the screw, the come-out phenomenon will occur frequently, and the screw groove may be broken easily. 
     Furthermore, the come-out phenomenon and the breakage of the screw groove may occur when loosening the screw, too. In this case, it becomes impossible to remove the screw without partly breaking the object to which the screw is fastened. Especially, when the screw groove is blocked with dust or others, the above-mentioned phenomenon occurs easily. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the present invention is to provide a screw, a driver bit and a header punch for manufacture of screw that can prevent the come-out phenomenon of the driver bit effectively by improving the configuration of the groove portion of the cross groove of the screw in the combination of the screw and the driver bit, so as to prevent the breakage of the screw that conventionally occurs, and to perform a correct and quick fastening of the screw normally even if the partial breakage occurs in the cross groove of the screw, so that the operation efficiency can be improved significantly. 
     In addition, another object of the present invention is to provide a combination of a plus-and-minus screw and a driver bit as well as a header punch for manufacture of screw that can prevent the come-out phenomenon of the driver bit effectively by improving the configuration of the groove portion of the bit fitting groove of the screw in the combination of the plus-and-minus screw and the driver bit, so as to prevent the breakage of the screw that conventionally occurs, and to perform a correct and quick fastening of the screw normally even if the partial breakage occurs in the bit fitting groove of the screw, so that the operation efficiency can be improved significantly. 
     A screw according to the first invention is characterized in that substantially vertical end wall portions of predetermined depth are formed on an end edge portion of a bit fitting groove on an screw head, non-planar bottom portions are raised from lower edge portions of the vertical end wall portions toward the center of the screw head, inclined groove portions are formed extending from the raised portions of the non-planar bottom portions toward the center of the screw neck, a substantially conical-shaped bottom surface is formed on the bottom of the groove, and the bit fitting groove is adapted to a driver bit that has a blade fitting in the bit fitting groove and abutting to the non-planar bottom portions at the lower edge. 
     In this case, the bit fitting groove in which the blade of the Phillips® screwdriver bit fits can be formed as a groove whose width is enlarged little by little from the center of the screw head to the outer portion in the radial direction, so that the angle between the opposing side walls of the neighboring grooves is a little smaller than 90 degrees. 
     A driver bit that is adapted to the screw is characterized in that a tip potion of the bit has a flat blade provided with substantially vertical end edge portions fitting in along the vertical end edge portion of the bit fitting groove of the screw head, and the tip edge surface of the blade is substantially horizontal surface with a protrusion formed at the center of the horizontal surface. 
     In this case, if the bit fitting groove of the screw, in which the blade of the Phillips® screwdriver bit fits, is formed as the groove whose width is enlarged little by little, the driver bit adapted to the screw preferably has the flat blade whose tip portion has side walls of the shape adapted to the groove whose width is enlarged little by little forming the bit fitting groove of the screw. 
     In addition, each end edge portion of the flat blade has the right-angled edge or an acute-angled edge crossing the horizontal surface of the blade tip and protruding a little in the horizontal surface side. 
     Furthermore, the protrusion formed at the center of the horizontal surface of the flat blade can be formed in the shape that is adapted to the inclined groove portions and the conical-shaped bottom surface formed at the center of the bit fitting groove of the screw. 
     A header punch for manufacture of the screws includes protrusions for forming the vertical edge wall portions of the bit fitting groove of the screw head and forming the non-planar bottom portions raised from the lower edge portion of the vertical edge wall portion toward the center of the screw head. The header punch also includes protruding lines for forming grooves extending with inclined or curved from the protrusion toward the center of the screw neck. 
     If the bit fitting groove of the screw is formed as the groove whose width is enlarged little by little, side walls of the protrusion for forming the bit fitting groove are preferably shaped to be adapted to the groove whose width is enlarged little by little. 
     According to the screw of the first invention having the above-mentioned configuration, substantially vertical end wall portions of predetermined depth are formed on an end edge portion of the bit fitting groove on an screw head, non-planar bottom portions are raised from lower edge portions of the vertical end wall portions toward the center of the screw head, inclined groove portions are formed extending from the raised portions of the non-planar bottom portions toward the center of the screw neck. Therefore, concerning the engagement of the blade tip of the driver bit with the bit fitting groove, a contact area of the tapered contact with the entire bit fitting groove is small. In addition, since the non-planar bottom surface is formed so that the area of the wall portions that the tip of the driver bit abuts at the boundary portion where the neighboring bit fitting grooves cross each other is enlarged, the come-out phenomenon of the driver bit is prevented securely. 
     In addition, the driver bit of the first invention includes a tip potion having a flat blade provided with substantially vertical end edge portions fitting in along the vertical end edge portion of the bit fitting groove of the screw head, and the tip edge surface of the blade is substantially horizontal surface with a protrusion formed at the center of the horizontal surface. Therefore, the driver bit that is the most adapted to the screw is provided. 
     Furthermore, the screw of the first invention can be manufactured easily by using the header punch having the protrusion and the protruding lines that are adapted to the contour of the bit fitting groove. 
     A plus-and-minus screw of the second invention has a bit fitting groove of a cross groove formed in the screw head. One of crossing linear grooves making up the bit fitting groove is formed so as to be adapted to a blade of a Phillips® screwdriver bit, while the other linear groove is formed so as to be adapted to a blade of a flat-blade driver bit. The plus-and-minus screw of the first invention is characterized in that substantially vertical wall portions having predetermined depth are formed at the end edge portion of the linear groove adapted to the blade of the Phillips® screwdriver bit, and the bit fitting groove is formed so as to be adapted to a driver bit having a blade that fits in one of the linear grooves and abuts the bottom of the groove at the lower edge when the blade tip of the Phillips® screwdriver bit engages the bit fitting groove. 
     In this case, the bottom portion of one of the linear groove adapted to the blade of the Phillips® screwdriver bit can have inclined groove portions extending from the lower edge of the vertical edge wall formed at the end edge portion of the groove toward the center of the screw head and a substantially conical-shaped bottom surface formed at the center bottom. 
     In addition, the bottom portion of one of the linear grooves can have a non-planar bottom portion raised from the lower edge of the vertical edge wall formed at the end edge portion of the linear groove toward the center of the screw head, inclined groove portions that extends from the raised portion of the non-planar bottom portion toward the center of the screw head, and a substantially conical-shaped bottom surface formed at the center bottom portion thereof. 
     Furthermore, the bottom portion of one of the linear groove can be formed as an inclined bottom surface inclined downward from the end edge portion of the of the vertical edge wall formed at the end edge portion of the groove toward the center of the screw neck, and a substantially conical-shaped bottom surface can be formed at the center bottom. 
     Furthermore, the bit fitting groove that the blade of the Phillips® screwdriver bit fits in and engages can have linear grooves, one of which is formed as a groove whose width is enlarged little by little from the center of the screw neck to the outer portion in the radial direction, and the width of the other linear groove is widened little by little from the center of the screw neck to the outer portion in the radial direction, so that an angle between the opposing wall portions of the neighboring grooves can be a little smaller than 90 degrees. 
     On the other hand, a driver bit adapted to the above-mentioned plus-and-minus screw is characterized in that a flat blade having substantially vertical end edge portions fitting in along the vertical wall portions of the linear groove of the screw head is provided to the tip portion, and the tip edge surface of the blade is substantially horizontal surface with a protrusion formed at the center of the horizontal surface. 
     If the bit fitting groove of the screw is formed as the groove whose width is enlarged little by little, the driver bit adapted to the screw preferably has the flat blade whose tip portion has side walls of the shape adapted to the groove whose width is enlarged little by little forming the bit fitting groove of the screw. 
     In addition, each end edge portion of the flat blade of the driver bit preferably has the right-angled edge or an acute-angled edge crossing the horizontal surface of the blade tip and protruding a little in the horizontal surface side. 
     Furthermore, the protrusion formed at the center of the horizontal surface of the driver bit is preferably formed in the shape that is adapted to the inclined groove portions and the conical-shaped bottom surface formed at the center of the bit fitting groove of the plus-and-minus screw. 
     A header punch for manufacture of the plus-and-minus screws includes protrusions crossing each other for forming the vertical edge wall portion of the bit fitting groove of the screw head and forming a predetermined groove bottom portion extending from the lower edge portion of the vertical edge wall portion toward the center of the screw head. The header punch also has protruding lines for forming the grooves extending with inclined or curved from the protrusions toward the center of the screw neck. 
     If the bit fitting groove of the screw is formed as the groove whose width is enlarged little by little, side walls of the protrusions for forming the bit fitting grooves are preferably shaped to be adapted to the groove whose width is enlarged little by little. 
     According to the plus-and-minus screw of the second invention having the above-mentioned configuration, substantially vertical end wall portions of predetermined depth are formed on an end edge portion of the bit fitting groove made of one of the linear grooves on an screw head. Therefore, concerning the engagement of the blade tip of the Phillips® screwdriver bit with the bit fitting groove, a contact area of the tapered contact with the linear groove is partial and small. In addition, since a bottom portion of the bit fitting groove is formed so that the area of the wall portions that the tip of the driver bit abuts is enlarged, the come-out phenomenon of the driver bit is prevented securely. 
     In addition the driver bit of the second invention includes a tip potion having a flat blade provided with substantially vertical end edge portions fitting in along the vertical end edge wall portion of the bit fitting groove consists of one of the linear grooves on the screw head, and the tip edge surface of the blade is substantially horizontal surface with a protrusion formed at the center of the horizontal surface. Therefore, the driver bit that is the most adapted to the plus-and-minus screw is provided. 
     Furthermore, the screw of the second invention can be manufactured easily by using the header punch having the protrusions and the protruding lines that are adapted to the contour of the bit fitting groove, especially one of the linear grooves. 
     Furthermore, a driver bit for a plus-and-minus screw of a third invention is a driver bit for a plus-and-minus screw adapted to a plus-and-minus screw having a bit fitting groove formed by a pair of linear grooves consist of an inclined groove portion and a horizontal groove portion crossing each other at the center of the screw head. The driver bit for a plus-and-minus screw is characterized in that the driver bit has a flat blade with an inclined end edge portions fitting in along the inclined groove portions of the plus-and-minus screw, and another flat blade crossing the flat blade perpendicularly to fit in along the horizontal groove of the plus-and-minus screw, and has a horizontal end edge portion extending substantially perpendicularly and abutting the bottom portion of the horizontal groove. The center portion of the tip of each blade is provided with a protrusion that fit in the conical-shaped bottom surface formed in the center of the screw head of the plus-and-minus screw. 
     In this case, the protrusion formed at the tip center of each flat blade can be formed in shape that is adapted to the groove portion and the conical-shaped bottom surface formed at the center of the bit fitting groove of the plus-and-minus 
     In addition, the flat blade that fits in along the horizontal groove of the plus-and-minus screw and has a horizontal end edge portion extending substantially perpendicularly to abut the bottom portion of the horizontal groove is preferably formed so that the width of the blade is adapted to the width of the horizontal groove. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of a side view of a principal portion showing an example of a screw according to the present invention. 
     FIG. 2 is a top view of the screw head shown in FIG.  1 . 
     FIG. 3 is a top view of the screw head showing another example of a screw according to the present invention. 
     FIG. 4 is a side view of a principal portion showing an example of a driver bit according to the present invention. 
     FIG. 5 is a side view of a principal portion showing a variation of the driver bit shown in FIG.  4 . 
     FIG. 6 is an explanatory cross section of a principal portion showing a connected state of a driver bit with the screw shown in FIG.  3 . 
     FIG. 7 is a cross section of a side view of a principal portion showing a connected state of the screw shown in FIG. 1 with the driver bit shown in FIG.  4 . 
     FIG. 8 is a cross section of a side view of a principal portion showing a variation of a connection state of the screw shown in FIG. 1 with the driver bit shown in FIG.  4 . 
     FIG. 9 is a cross section of a side view of a principal portion showing another example of a screw according to the present invention. 
     FIG. 10 is a cross section of a side view of a principal portion showing still another example of a screw according to the present invention. 
     FIG. 11 is a cross section of a principal portion showing a header punch for manufacture of screws used for forming the screw head shown in FIG.  1 . 
     FIG. 12 is a side view of a principal portion showing a header punch for manufacture of screws used for forming the screw head shown in FIG.  9 . 
     FIG. 13 is a top view of a screw head showing an example of a plus-and-minus screw according to the present invention. 
     FIG. 14 is a cross section of a side view of a principal portion along the XIV—XIV line of the plus-and-minus screw shown in FIG.  13 . 
     FIG. 15 is a cross section of a side view of a principal portion showing a variation of the plus-and-minus screw shown in FIG. 14 
     FIG. 16 is a top view of a screw head showing another example of a plus-and-minus screw according to the present invention. 
     FIG. 17 is a cross section of a side view of a principal portion along the XVII—XVII line of the plus-and-minus screw shown in FIG.  16 . 
     FIG. 18 is a top view of a screw head showing still another example of a plus-and-minus screw according to the present invention. 
     FIG. 19 is a side view of a principal portion showing an example of a driver bit adapted to a plus-and-minus screw according to the present invention. 
     FIG. 20 is a side view of a principal portion showing a variation of the driver bit shown in FIG.  19 . 
     FIG. 21 is a cross section of a side view of a principal portion showing a connection state of the plus-and-minus screw shown in FIG.  15  and the driver bit shown in FIG.  19 . 
     FIG. 22 is an explanatory top view of a screw head showing a connection state of the driver bit shown in FIG. 19 at the screw head of the plus-and-minus screw shown in FIG.  13 . 
     FIG. 23 is an explanatory plane view of a principal portion showing a connection state with the driver bit adapted to the plus-and-minus screw shown in FIG.  18 . 
     FIGS.  24 ( a ) to  24 ( c ) are a front view of a principal portion, a left side view of a principal portion and a top view of a header punch for manufacture of screws for forming a screw head of the plus-and-minus screw shown in FIG.  13 . 
     FIGS.  25 ( a ) and  25 ( b ) are a front side view of a principal portion and a left side view of a principal portion showing another example of a driver bit for a plus-and-minus screw according to the present invention. 
     FIG. 26 is a side view of a principal portion showing a variation of the driver bit for a plus-and-minus screw shown in FIG.  25 . 
     FIGS.  27 ( a ) and  27 ( b ) are cross sections of side views of principal portions showing connection states of the driver bit for a plus-and-minus screw shown in FIG. 25 with the conventional plus-and-minus screws shown in FIGS. 33 and 34, respectively. 
     FIG. 28 is an explanatory top view of the screw head showing a connection state of the driver bit for a plus-and-minus screw shown in FIG. 27 and a plus-and-minus screw. 
     FIG. 29 is a cross section of a side view of a principal portion of a conventional screw having a cross groove. 
     FIG. 30 is a top view of the screw head of the screw having a cross groove shown in FIG.  29 . 
     FIG. 31 is a side view of a principal portion of a driver bit for a screw having a cross groove. 
     FIG. 32 is a cross section of a side view of a principal portion showing a connection state of the screw shown in FIG.  29  and the driver bit shown in FIG.  31 . 
     FIG. 33 is a cross section of a side view of a principal portion of a conventional plus-and-minus screw. 
     FIG. 34 is a top view of the plus-and-minus screw shown in FIG.  33 . 
     FIG. 35 is a cross section of a side view of a principal portion showing a connection state of the plus-and-minus screw shown in FIG.  33  and the driver bit shown in FIG.  31 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. 
     FIRST EXAMPLE 
     Screw ( 1 ) 
     FIGS. 1 and 2 show an example of a screw according to the present invention. Namely, in FIGS. 1 and 2, reference numeral  30  shows a screw of the present invention. A screw head  30   a  of the screw  30  includes a head or top surface  30   c  extending along a direction substantially perpendicular to a central axis of the screw  30  and is provided with bit fitting grooves  32 . The bit fitting grooves  32  are arranged to cross each other like a plus (+) mark at the center of the screw head  30   a.    
     This bit fitting groove  32  has a configuration in which a vertical end wall portion  32   a  having a predetermined depth is formed at the end edge portion of the groove, a inclined bottom portion  32   b  is formed, which is raised from a lower edge portion  32   a ′ of the end wall portion  32   a  toward a central axis of the screw head  30   a , an inclined groove portion  32   c  is formed from the raised portion  32   b ′ of the inclined bottom portion  32   b  so as to extend toward the central axis of the screw head portion  30   b , and a substantially conical-shaped bottom surface  34  having a gentle slope at the bottom portion is formed. 
     Reference numeral  33  denotes a substantially vertical side wall portion having an angle of 1.5-2.0 degrees so as to form an appropriate draft, which corresponds to a taper of a header punch formed on neighboring side wall portions of the bit fitting grooves  32 . Therefore, this side wall portion  33  abuts and engages the side wall portion of the blade of a driver bit mentioned below. 
     In addition, at each corner adjacent to the bit fitting grooves  32 , similarly to the conventional screw with cross groove shown in FIG. 30, tapered connection surfaces  37   a  and  37   b  are formed, which extends from the position of the conical-shaped bottom surface  34  to the opening end of the bit fitting groove  32  at the screw head  30   a.    
     As mentioned above, the screw  30  of the present example has inclined bottom portions  32   b  at the end edge portions of the bit fitting groove  32 , inclined groove portions  32   c  that extend from the raised portion  32   b ′ of the non-planar bottom portion  32   b  toward the center of the screw head portion  30   b . Therefore, tapered contact area of the entire bit fitting groove  32  is partial and small. In addition, the area of the side wall portion  33  to which a tip of a drive bit abuts at the boundary between the neighboring bit fitting grooves  32  and  33  (the area of the driving surface that the driver bit apply a rotation drive force to the screw) can be enlarged. 
     In addition, the width of the bit fitting groove  32  is adapted to the thickness of the blade of the driver bit mentioned below. The width is preferably a little larger than the above mentioned thickness in consideration of plating or coating of the surface of the screw. 
     Screw ( 2 ) 
     FIG. 3 shows another example of the screw  30  of the present invention. In this example, at the opposing side wall portions  33  of the bit fitting groove  32  of the screw  30 , the width is enlarged little by little from the central axis of the screw head  30   a  to the outer portion in the radial direction so as to form tapered sidewall portions  33   a  and  33   b  of grooves  32 . 
     As mentioned above, the screw  30  of the present example has tapered sidewall portions  33   a  and  33   b  of grooves  32  whose width is enlarged little by little, so that the opening angle β of the opposing side wall portions of the neighboring grooves is set a little smaller than 90 degrees. Thus, in combination with a driver bit mentioned below, come-out phenomenon from the bit fitting groove  32  of the screw  30  can be prevented effectively. 
     Driver Bit ( 1 ) 
     FIG. 4 shows an example of a driver bit  40  adapted to the screw  30  explained with reference to FIGS. 1 to  3 . The driver bit  40  of the present example has a blade  42  that engages the bit fitting grooves  32  of the screw  30 , and have horizontal surfaces  42   a , alternatively referred to as tip surfaces extending substantially perpendicularly to engage the vertical end wall portions  32   a  and the (non-planar) bottom portions  32   b  formed at the end edge portions of the bit fitting grooves  32 . The driver bit  40  also has a number of protrusions. For example, the driver bit  40  has four protrusions in one embodiment, with the three protrusions  42   b   1 ,  42   b   2 , and  42   b   3  shown in FIG.  4 . These protrusions are adapted to the inclined groove portions  32   c  extending from the raised portions  32   b ′ of the non-planar bottom portions  32   b  of the bit fitting groove  32  toward the center of the screw neck  30   b.    
     Reference numeral  43  denotes a substantially vertical side wall portions with a permitted little taper formed at both side surfaces of the blades  42  or the horizontal surface portions  42   a . These side wall portions  43  abut and engage the side wall portions  33  formed at the bit fitting grooves  32  of the screw  30  mentioned above. Therefore, engagement of these driving surfaces can provide sufficient engaging area, so that the come-out phenomenon that occurs in the conventional combination of screw and driver bit can be prevented effectively. 
     Furthermore, in the above-mentioned screw  30 , the tapered connection surfaces  37   a  and  37   b  are formed at the neighboring corner portions of the bit fitting groove  32  in the same way as the conventional screw. Therefore, even if the conventional driver bit for screws with cross groove as shown in FIG. 31 is used, for example, a part of the blade of the drive bit abuts and engages the tapered connection surfaces  37   a  and  37   b , so as to achieve the operation of fastening the screw. 
     Driver Bit ( 2 ) 
     FIG. 5 shows a variation of the driver bit  40  shown in FIG.  4 . At each end edge portion  42   a ′ of the blade  42  of the driver bit  40  of the above-mentioned example, the edge portion crossing the horizontal surface portion  42   a  of the blade tip, in this variation, forms an acute-angled edge that defines an inclined surface protruding from the horizontal surface portion  42   a  side, and the protrusion  42   b  is formed as a vertical protrusion  42   c  protruding downward. Namely, the driver bit  40  of this example has the vertical protrusion  42   c , which is formed not to perform tapered contact with the inclined groove portion  32   c  of the bit fitting groove  32  of the screw  30  explained in the above-mentioned example. Thus, the driver bit  40  ensures the prevention of the come-out phenomenon. 
     Drive Bit ( 3 ) 
     FIG. 6 shows an example of the driver bit  40  adapted to the screw, especially the screw  30  of the example shown in FIG.  3 . Basic configuration of the driver bit  40  is the same as the example shown in FIG. 4 or  5 . In this case, the driver bit  40  is adapted to the screw having the bit fitting groove  32  formed as the grooves  33   a  and  33   b  whose width is enlarged little by little. The side wall potions  43  at the tip of the flat blade  42  are formed as side wall portions  43   a  and  43   b  having width widened little by little, which are adapted to the grooves  33   a  and  33   b  whose width is enlarged little by little. Therefore, when the blade  42  of the driver bit  40  abuts the side wall portions of the bit fitting groove  32  of the screw  30 , clearance between the grooves  33   a ,  33   b  and the side wall portions  43   a ,  43   b  can be minimized so that a proper engagement of the bit with the screw can be achieved. 
     In addition, according to this example, upon fastening the screw, torque transmission with balance can be achieved, since the opening angle β between the opposing side wall portions of the neighboring grooves is set a little smaller than 90 degrees as shown in FIG. 3 when the bit fitting groove  32  of the screw  30  having the grooves  33   a  and  33   b  whose width is enlarged little by little abuts the side wall portions (T 1 , T 2 , T 3  and T 4 ). Further in this case, the torque τ 1  applied to the side wall portions (T 1 , T 2 , T 3  and T 4 ) can be directed to the screw neck portion side than a tangent direction τ 0  of the screw head  30   a  to which the blade  42  of the driver bit  40  act. Thus, the com-out phenomenon can be prevented efficiently. This is also true when the driver bit  40  shown in FIG. 4 and 5 or the conventional driver bit  20  shown in FIG. 31 is used. 
     Combination of a Screw and a Driver Bit ( 1 ) 
     FIG. 7 shows operation of engagement of the screw  30  mentioned above (see FIG. 1) and the driver bit  40  (see FIG.  3 ). According to this example, the horizontal surface  42   a  and the protrusion  42   b  formed of the flat blade  42  of the driver bit  40  fit in the non-planar bottom portions  32   b  and the inclined groove portions  32   c  of the bit fitting groove  32  of the screw  30 . The side wall portions  43  of the blades  42  and the protrusion  42   b  abut the side wall portions  33  of the bit fitting groove  32  of the screw  30 . Thus, a desired torque can be transmitted to the screw  30  by rotating the driver bit  40 . 
     Especially, according to the present example, since the non-planar bottom portions  32   b  is formed in the bit fitting groove  32  of the screw  30 , the contact area of the side wall portions  33  contacting the side wall portion  43  of the flat blade  42  of the driver bit  40  can be enlarged upon engagement with the driver bit  40 . In addition, the tapered contact area of the protrusion  42   b  of the driver bit  40  abutting the inclined groove portions  32   c  of the bit fitting groove  32  of the screw  30  is partial and small. Therefore, the come-out phenomenon that occurs in the conventional combination of screw and driver bit can be securely prevented. 
     Combination of a Screw and a Driver Bit ( 2 ) 
     FIG. 8 shows a variation of the engagement operation of the screw  30  shown in FIG.  7  and the driver bit  40 . In this example, the flat blade  42  of the driver bit  40  (bit axis L 1 ) is engaged with the bit fitting groove  32  of the screw head  30   a  at a predetermined slant angle θ with respect to the screw axis L 0 . Also in this combination of the screw  30  and the driver bit  40 , accordance with the present invention, a predetermined torque is transmitted to the screw  30  when the driver bit  40  is rotated in the same way as the above-mentioned example. In this case, an allowable angle θ between the screw axis L 0  and the bit axis L 1  is preferably less than about 15 degrees. 
     Screw ( 3 ) 
     FIG. 9 shows another example of the screw according to the present invention. For easiness of the explanation, the same portion as the screw shown in FIG. 1 is denoted by the same reference numeral, and the detail explanation of the element is omitted. In this example, the present invention is applied to a screw with a pan-shaped screw head  30   a  instead of the plate-shaped screw head  30   a  shown in FIG.  1 . The screw  30  of the present example has a lower edge portion of the vertical end wall portion  32   a  formed at the end edge portion of the bit fitting groove  32 . The lower edge portion is shallower than the example shown in FIG.  1 . An inclined portion  32   a ″ is formed inclining downward at first from the lower edge portion toward the center of the screw head  30   a . Then, the upward raised portion  32   b ′ is formed. Other configuration is basically the same as the screw shown in FIG.  1 . 
     By using the screw  30  of this example too, a proper screw fastening operation can be performed without the come-out phenomenon in the combination with the driver bit  40  of the above-mentioned example. 
     Screw ( 4 ) 
     FIG. 10 shows still another example of the screw according to the present invention. In this example too, the same portion as the screw shown in FIG. 1 is denoted by the same reference numeral, and the detail explanation of the element is omitted for easiness of the explanation. The screw  30  of the present example, similarly to the example shown in FIG. 9, is the one having a pan-shaped screw head  30   a  to which the present invention is applied. The upper edge portion of the vertical end wall portion  32  a formed at the end edge portion of the bit fitting groove  32  is opened with a predetermined taper  32   d . Other configuration is basically the same as the screw shown in FIG.  1 . 
     According to the above-mentioned configuration, even if a driver bit  20  shown in FIG. 31, for example, for the conventional screw with a cross groove is used, the blade of the driver bit  20  is properly engaged with the tapered portion  32   d  of the upper edge portion of the vertical end wall portion  32   a , and also engaged properly with the bit fitting groove  32  of the screw  30  of this example. 
     Header Punch ( 1 ) 
     FIG. 11 shows an example of the header punch  50  for manufacture of the screw  30  of the example shown in FIG.  1 . The header punch  50  of this example is used for punching the bit fitting groove  32  in the screw head  30   a  of the screw  30  shown in FIG.  1 . The header punch  50  of this example has protrusions  52  with protruding edge portions  52   a  for forming the vertical end wall portions  32   a  and the bottom portions  32   b  at the end edge portion of the bit fitting groove  32  of the screw head  30   a , and an inclined protrusion line  52   b  for forming the inclined groove portions  32   c  extending from the protrusions  52  toward the center of the screw neck  30   b.    
     Header Punch ( 2 ) 
     The header punch for manufacture of the screw  30  of the example shown in FIG. 3 is structured by making the side wall portions  53  of the protrusion  52  of the header punch shown in FIG. 11 for forming the grooves  33   a  and  33   b  of the bit fitting groove whose width is enlarged little by little such that the width is enlarged little by little from the center of the protrusion  52  to the outer portion in the radial direction in the configuration of the header punch  50  shown in FIG.  11 . Thus, the header punch can easily manufacture the screws  30  of the example shown in FIG.  3 . 
     Header Punch ( 3 ) 
     FIG. 12 shows an example of the header punch for manufacture of the screw  30  of the example shown in FIG.  9 . For easiness of the explanation, the same portion as the header punch shown in FIG. 11 is denoted by the same reference numeral, and the detail explanation of the element is omitted. The header punch  50  of this example has protrusions  52  with protruding edge portions  52   a ″ for forming the vertical end edge portions  32   a  and the non-planar bottom portions  32   b  at the end edge portion of the bit fitting groove  32  of the screw head  30   a , and an inclined protrusion line  52   b  for forming the inclined groove portions  32   c  extending toward the center of the screw neck  30   b  by the protrusions  52 . 
     Second Example 
     Next, a combination of a plus-and-minus screw and a driver bit as well as a header punch for manufacture of the screw of a second example according to the present invention will be explained in detail with reference to the attached drawings. 
     [Plus-an] Plus-and-minus Screw ( 1 ) 
     FIGS. 13 and 14 show an example of a plus-and-minus screw according to the present invention. In FIGS. 13 and 14, reference numeral  60  denotes the plus-and-minus screw according to the present invention. The screw head  60   a  of the plus-and-minus screw  60  is provided with a bit fitting groove  62 . This bit fitting groove  62  consists of a pair of linear grooves  62   a  and  62   b  that cross each other like a plus (+) mark at the center of the screw head  60   a.    
     In the bit fitting groove  62  of this example, one of the linear grooves  62   a  forms a vertical end wall portion  63   a  having a predetermined depth at the end edge portion of the groove, a groove bottom portion  63   b  extending from a lower edge portion  63   a ′ of the end wall portion  63   a  toward the center of the screw head  60   a  forms a horizontal bottom portion, and an inclined groove portion  63   c  is formed from the horizontal bottom portion ( 63   b ) toward the center of the screw neck  60   b . The center bottom portion is provided with a substantially conical-shaped bottom surface  64 . A substantially vertical side wall portion  65   a  having an angle of 1.5-2.0 degrees as an appropriate draft (for draught of a header punch) formed at each side of the linear groove  62   a . This side wall portion  65   a  abuts and engage a side wall portion of a Phillips® screwdriver bit mentioned below. 
     The other linear groove  62   b  is formed and extended as a horizontal groove ( 62   b ) having an adequate width and depth for abutting and engaging the blade of a flat-blade screwdriver bit. In the same way as the above-mentioned linear groove  62   a , a substantially vertical side wall portion  65   b  having an angle of 1.5-2.0 degrees as an appropriate draft (for draught of a header punch) formed at each side of the horizontal groove ( 62   b ). The side wall portion  65   b  abuts and engages the blade of the known flat-blade screwdriver bit. 
     Corner portions between the linear groove  62   a  and the neighboring linear groove (the horizontal groove)  62  is provided with taper connection surfaces  67   a  and  67   b  in the same way as in the conventional plus-and-minus screw shown in FIG.  34 . 
     As mentioned above, the plus-and-minus screw  60  of this example has the vertical end wall portion  63   a  at the end edge portion of the one linear groove  62   a  and groove bottom portion  63   b  formed as a horizontal bottom portion  63   b . The inclined groove portions  63   c  are formed extending from the horizontal bottom portions  63   b  toward the center of the screw neck  60   b . Thus, the tapered contact area of the entire bit fitting groove  62  is partial and small. In addition, the area of the side wall portion  65   a  of the one linear groove  62   a  of the opposing bit fitting groove  62  to which a tip of a drive bit abuts (the area of the driving surface that the driver bit apply a rotation drive force to the screw) can be enlarged. 
     In addition, the groove width of the one linear groove  62   a  is adapted to the thickness of the blade of the driver bit mentioned below and is preferably a little wider than the thickness in consideration of the plating or coating on the surface of the screw. 
     [Plus-an] Plus-and-minus Screw ( 2 ) 
     FIG. 15 shows a variation of the plus-and-minus screw  60  shown in FIGS. 13 and 14. In this example, the groove bottom portion  63   b  of one linear groove  62   a  of the bit fitting groove  62  has a non-planar bottom portions ( 63   b ) raised from the lower edge portion  63   a ′ of the vertical end wall portion  63   a  having a predetermined depth formed at the end edge portion toward the center portion of the screw head portion  60   a  and an inclined groove portions  63   c  extending from the non-planar bottom portions  63   b  toward the center portion of the screw neck portion  60   b  so that the center bottom portion is formed as a substantially conical-shaped bottom surface  64  having a mild slope. Other configuration is the same as the plus-and-minus screw  60  of the example mentioned above. 
     The plus-and-minus screw  60  of this example, in the same way as the above-mentioned example, makes the tapered contact area of the entire bit fitting groove  62  partial and small. In addition, the contact area of the side wall portions  65   a  of the one linear groove  62   a  of the opposing bit fitting groove  62  to which the tip of the driver bit abuts can be enlarged. 
     [Plus-an] Plus-and-minus Screw ( 3 ) 
     FIGS. 16 and 17 show still another example of the plus-and-minus screw  60  according to the present invention. In this example, the groove bottom portion  63   b  of one linear groove  62   a  of the bit fitting groove  62  has an inclined groove portion ( 63   b ) inclined from the lower edge portion  63   a ′ of the vertical end wall portion  63   a  having a predetermined depth formed at the end edge portion toward the center portion of the screw head portion  60   a , so that the center bottom portion is formed as a substantially conical-shaped bottom surface  64  having a mild slope. 
     Other configuration is the same as the plus-and-minus screw  60  of the example mentioned above. The plus-and-minus screw  60  of this example, in the same way as the above-mentioned example, makes the tapered contact area of the entire bit fitting groove  62  partial and small. In addition, the contact area of the side wall portions  65   a  of the one linear groove  62   a  of the opposing bit fitting groove  62  to which the tip of the driver bit abuts can be enlarged. 
     [Plus-an] Plus-and-minus Screw ( 4 ) 
     FIG. 18 shows still another example of the plus-and-minus screw  60  according to the present invention. In this example, the one linear groove  62   a  and the other linear groove  62   b  of the plus-and-minus screw  60  are formed as grooves  62   a ′ and  62   b ′ whose groove width are substantially widened little by little from the center portion of the screw head  60   a  to the outer portion in the radial direction. 
     In the plus-and-minus screw  60  of this example having the above-mentioned configuration, equal clearances δ are formed as shown in the figure when the blade (illustrated by the broken line) of the driver bit abuts the side walls of the bit fitting groove  62  of the plus-and-minus screw  60 , since the above-mentioned groove  62   a ′ and  62   b ′ whose width is enlarged little by little are formed. Therefore, the blade of the driver bit can abut the side wall portions (T 1  and T 2 ) of the one groove  62   a ′ and the side wall portions (T 3 ′ and T 4 ′) of the other groove  62   b ′ simultaneously, so that a balanced torque transmission can be achieved. 
     Furthermore, in the same way as the screw  30  of the example mentioned above with reference to FIG. 3, the plus-and-minus screw  60  of this example also can prevent the come-out phenomenon from the bit fitting groove  62  of the plus-and-minus screw  60  in the combination with a driver bit mentioned below by setting the opening angle β of the opposing side wall portions of the neighboring grooves a little smaller than 90 degrees. 
     Driver Bit ( 1 ) 
     FIG. 19 shows an example of a driver bit  70  adapted to the screw  60  of the example explained with reference to FIGS. 13 to  18 . The driver bit  70  of the present example has a flat blades  72  that engage the bit fitting grooves  62  of the screw  60 , and have horizontal surfaces  73   a  extending substantially perpendicularly to engage the vertical end wall portions  63   a  and the non-planar bottom portions  63   b  formed at the end edge portions of the one linear groove  62   a  of the bit fitting grooves  62 . The driver bit  70  also has a protrusions  73   b  adapted to the contour of the inclined groove portions  63   c  extending from the groove bottom portions  63   b  of the linear groove  62   a  toward the center of the screw neck  60   b.    
     Reference numeral  75  denotes a substantially vertical side wall portions with a permitted little taper formed at both side surfaces of the flat blades  72  or the horizontal surface portions  73   a . These side wall portions  75  abut and engage the side wall portions  65   a  formed at the one linear groove  62   a  of the bit fitting grooves  62  of the plus-and-minus screw  60  of the above-mentioned example. 
     Therefore, engagement of these driving surfaces can provide sufficient engaging area, so that the come-out phenomenon that occurs in the combination of the conventional plus-and-minus screw and driver bit can be prevented effectively. 
     Furthermore, the screw  60  of the above-mentioned example has the tapered connection surfaces  67   a  and  67   b  formed at the neighboring corner portions of the linear grooves  62   a  and  62   b  of the bit fitting groove  62  in the same way as the conventional plus-and-minus screw  60 . Therefore, even if the conventional driver bit as shown in FIG. 31 is used, for example, a part of the blade of the drive bit abuts and engages the tapered connection surfaces  67   a  and  67   b , so as to achieve the operation of fastening the screw. 
     Driver Bit ( 2 ) 
     FIG. 20 shows a variation of the driver bit  70  shown in FIG.  19 . At each end edge portion  73   a ′ of the flat blade  72  of the driver bit  70  of the above-mentioned example, the edge portion crossing the horizontal surface portion  73   a  of the blade tip is formed in acute angle protruding in the horizontal surface portion  73   a  side, and the protrusion  73   b  is formed as a vertical protrusion  73   c  protruding downward. Namely, the driver bit  70  of this example has the vertical protrusion  73   c , which is formed not to perform tapered contact with the inclined groove portion  63   c  of the one linear groove  62   a  of the plus-and-minus screw  60  explained in the above-mentioned example. Thus, the driver bit  70  having the above-mentioned configuration ensures the prevention of the come-out phenomenon. 
     Combination of a Plus-and-minus Screw and a Driver Bit ( 1 ) 
     FIG. 21 shows operation of engagement of the plus-and-minus screw  60  of the above-mentioned example (see FIG. 15) and the driver bit  70  (see FIG.  19 ). According to this example, the horizontal surface  73   a  and the protrusion  73   b  formed of the flat blade  72  of the driver bit  70  fit in the groove bottom portions  63   b  and the inclined groove portions  63   c  of the one linear groove  62   a  of the plus-and-minus screw  60 , so that the side wall portions  75  of the blades  72  and the protrusion  73   b  can abut the side wall portions  65   a  of the one linear groove  62   a  of the plus-and-minus screw  60  (see FIG.  22 ). Therefore, a desired torque can be transmitted to the plus-and-minus screw  60  at the abutting portions (T 1  and T 2 ) of the blade  72  of the driver bit  70  with the one linear groove  62   a  of the plus-and-minus screw  60  by rotating the driver bit  70  in the direction of the arrow as shown in FIG.  22 . In this case, concerning the relationship of the other linear groove  62   b  of the plus-and-minus screw  60  and the blade  72  of the driver bit  70 , the blade  72  cannot abut the side wall portions  65   b  (T 3  and T 4 ) of the other linear groove  62   b  (see FIG.  22 ). 
     Especially, according to the present example, in the case where the non-planar bottom portions  63   b  is formed in the one linear groove  62   a  of the bit fitting groove  62  of the screw  60 , the contact area of the side wall portions  65   a  contacting the side wall portion  75  of the flat blade  72  of the driver bit  70  can be enlarged upon engagement with the driver bit  70 . In addition, the tapered contact area of the protrusion  73   b  of the driver bit  70  abutting the inclined groove portions  63   c  of the one linear groove  62   a  of the plus-and-minus screw  60  is partial and small. Therefore, the come-out phenomenon that occurs in the conventional combination of plus-and-minus screw and driver bit can be securely prevented (see FIG.  21 ). 
     Combination of a Plus-and-minus Screw and a Driver Bit ( 2 ) 
     FIG. 23 shows an engagement operation of the driver bit  70  adapted to the plus-and-minus screw  60  especially shown in FIG.  18 . In this example, the driver bit  70  used for the plus-and-minus screw  60  having the bit fitting groove  62  formed as grooves  62   a ′ and  62   b ′ whose width is substantially enlarged little by little, has side wall portions  75  at the tip of the flat blade  72 . The side wall portions  75  is formed as side wall portions  75   a  and  75   b  whose width is enlarged little by little to as to be adapted to the grooves  62   a ′ and  62   b ′ whose width is enlarged little by little. Thus, a clearance between the grooves  62   a ′,  62   b ′ and the side wall portions  75   a ,  75   b  can be minimized when the blade  72  of the driver bit  70  abuts the side wall portions of the bit fitting grooves  62  of the plus-and-minus screw  60 , so that a proper engagement of the bit with the plus-and-minus screw can be achieved. 
     In addition, in the same way as the screw  30  of the example explained above with reference to FIG. 6, the torque τ 1  applied to the side wall portions of the bit fitting groove  62  of the plus-and-minus screw  60  can be directed to the screw neck portion side than a tangent direction τ 0  of the screw head  60   a  to which the blade  72  of the driver bit  70  act. Thus, the com-out phenomenon can be prevented efficiently. 
     Header Punch ( 1 ) 
     A header punch for manufacture of the plus-and-minus screw  60  of the example explained above with reference to FIGS. 13 and 14, FIGS. 15 and 16, or FIG. 17 can be made similarly to the header punch  50  of the first example explained above (see FIGS.  11  and  12 ). 
     As shown in FIGS.  24 ( a ) to  24 ( c ), the header punch of this example has protrusions  92   a  and  92   b  with raised portions  93  for, forming vertical end edge portions  63   a  and groove bottom portions  63   b  (horizontal bottom portions, non-planar bottom portions and inclined bottom portions) at the end edge portions of the bit fitting groove  62  of the screw head portion  60   a . The protrusions  92   a  and  92   b  correspond to the pair of linear grooves  62   a  and  62   b  that cross each other. The header punch also has inclined protrusion lines  93   c  for forming the inclined groove portions  63   c  extending from the protrusions toward the center portion of the screw neck  60   b.    
     Header Punch ( 2 ) 
     Further more, especially a header punch for manufacture of the plus-and-minus screw  60  of the example shown in FIG. 18 is structured by making the side wall portions (see  95   a  and  95   b  of FIG. 24) of the protrusion (see  92   a  and  92   b  of FIG. 24) that form the grooves  62   a ′ and  62   b ′ of the bit fitting groove  62  whose width is enlarged little by little in the structure of the header punch  50  for manufacture of the plus-and-minus screw  60  of the above-mentioned example such that the width is enlarged little by little from the center portion of the protrusion toward the outer portion in the radial direction. Thus, the header punch can easily manufacture the plus-and-minus screws  60  of the example shown in FIG.  18 . 
     THIRD EXAMPLE 
     Further, the driver bit for the plus-and-minus screw as a third example of the present invention will be explained in detail with reference to the attached drawings. 
     Driver Bit ( 1 ) 
     FIG. 25 shows an example of a driver bit for the plus-and-minus screw according to the present invention. In FIGS.  25 ( a ) and  25 ( b ), reference numeral  80  denotes a configuration of a principal portion of the driver bit for plus-and-minus screw according to the present invention. The blade tip of the driver bit  80  is adapted to the bit fitting groove  12  or  62  formed by a pair of linear grooves  12   a  and  12   b  or  62   a  and  62   b  crossing each other at the center portion of the screw head  10   a  or  60   a  of the plus-and-minus screw  60  shown in FIGS. 15 to  18 , or the conventional plus-and-minus screw  10  shown in FIGS. 33 and 34. The driver bit  80  of the present example has a flat blades  82  that engage the bit fitting grooves  12  or  62  of the screw  10  or  60 , and has an inclined end edge portion  83   a  that engages the inclined groove formed as the one linear groove  12   a  or  62   a , and a flat blade  84  that has a horizontal end edge portion  85   a  extending substantially perpendicularly to engage the horizontal groove portions formed as the other linear end edge portion  12   b  or  62   b.    
     In addition, the tip center portion of the flat blades  82  and  84  are provided with a protrusion  86  having vertical surface portions  83   b  and  85   b  for fitting in the conical-shaped bottom surface  14  and  64  formed at the center of the screw head  10   a  or  60   a  of the plus-and-minus screw  10  or  60 . The both side surfaces of the flat blades  82  and  84  are formed as substantially vertical side wall portions  87  and  88  with some taper permitted. 
     The protrusion  86  provided at the tip center portion of the flat blades  82  and  84  can be structured to have inclined surface portions  83   c  and  85   c  as shown in FIG.  26 . 
     Combination with a Plus-and-minus Screw ( 1 ) 
     The driver bit  80  of this example having the above-mentioned configuration, with respect to the plus-and-minus screw  10  shown in FIGS. 28 and 29 or the plus-and-minus screw  60  shown in FIGS. 15-18, concerning the bit fitting groove  12  or  62 , as shown in FIGS. 27 and 28, the flat blades  82  and  84  can be engaged with the corresponding grooves  12   a  and  12   b  or  62   a  and  62   b.    
     Namely, for the plus-and-minus screw  10  shown in FIGS. 28 and 29, the one flat blade  82  can be engaged with the inclined groove portion  12   a  that is the one linear groove of the bit fitting groove  12  properly as shown in FIG.  27 ( a ). In this case, the inclined end edge portion  83   a  and the protrusion  86  formed on the flat blade  82  of the driver bit  80  fit in the inclined groove  12   a  of the plus-and-minus screw  10 , so that the side wall portion  87  of the flat blade  82  and the protrusion  86  can be abut the side wall portion  16   a  of the inclined groove portions  12   a  of the plus-and-minus screw  10 . Therefore, a desired torque can be transmitted to the plus-and-minus screw  10  at the abutting portions (T 1  and T 2 ) of the blade  82  of the driver bit  80  with the inclined groove  12   a  of the plus-and-minus screw  10  by rotating the driver bit  80  in the direction of the fastening (see FIG.  28 ). 
     In addition, the other flat blade  84 , as shown in FIG.  27 ( b ), can be engaged correctly with the horizontal groove portion  12   b  that is the other linear groove of the bit fitting groove  12 . In this case, the horizontal end edge portion  85   a  and the protrusion  86  formed on the flat blade  84  of the drover bit  80  fit in the horizontal groove  12   b  of the plus-and-minus screw  10 . Thus, the side wall portion  88  of the blade  84  and the protrusion  86  can abut the side wall portion  16   b  of the horizontal groove portions  12   b . Therefore, a desired torque can be transmitted to the plus-and-minus screw  10  at the abutting portions (T 3  and T 4 ) of the blade  84  of the driver bit  80  with the horizontal groove  12   b  of the plus-and-minus screw  10  by rotating the driver bit  80  in the direction of the fastening (see FIG.  28 ). 
     Especially, in this example, as shown in FIG.  27 ( b ), the driving contact and engagement of the side wall portion  16   b  formed at the horizontal groove portions  12   b  of the plus-and-minus screw  10  with the side wall  88  of the flat blade  34  can obtain a sufficient contact area compared with the conventional Phillips® screwdriver bit. Therefore, the come-out phenomenon in the screw fastening operation (see FIG. 35) can be prevented effectively. 
     In addition, according to the driver bit  80  of the present example, a part of each blade  82  or  84  of the driver bit  80  abuts and engages the tapered connection surfaces  17   a  and  17   b  formed at the corner portions of the neighboring linear grooves  12   a  and  12   b  of the bit fitting groove. Thus, a sufficient torque is transmitted so that correct and secure screw fastening can be achieved. 
     Therefore, the driver bit  80  of this example having the above-mentioned configuration can transmit a sufficient torque to the liner grooves  62   a  and  62   b  of the bit fitting groove  62  also for the plus-and-minus screw  60  shown in FIGS. 15-18, in the same way as mentioned above, by a part of the blades  82  and  84  of the driver bit  80  abuts and engages the liner grooves  62   a  and  62   b , so that correct and secure screw fastening operation can be achieved. 
     In addition, in the driver bit  80  for the plus-and-minus screw of this example, the blade width (thickness) of the blades  82  and  84  crossing each other is normally set identical to each other. However, the groove width of the horizontal groove portion  12   b  is set wider than the width of the inclined groove in a bit fitting groove  12  of the general plus-and-minus screw  10  (see FIG.  28 ). Therefore, if the width of the blade  84  of the driver bit  80  engaging the horizontal groove portion  12   b  is set thick so as to be adapted to the groove width of the horizontal groove  12   b , simultaneous contact can be performed at the contact portion (T 1  and T 2 ) between the blade  82  and the inclined groove portion  12   a , as well as the contact portion (T 3  and T 4 ) between the blade  84  and the horizontal groove portion  12   b . Thus, the most effective torque transmission can be achieved. 
     Therefore, according to the driver bit for the plus-and-minus screw of the present invention, for the loosening operation of the screw apposite to the screw fastening operation mentioned above, the torque transmission similar to the above explanation can be performed, so that correct and secure loosening of screws can be achieved. 
     Though preferred examples of the present invention are explained, the present invention is not limited to the examples. Various modifications can be performed within the spirit of the present invention. 
     The screw of the first example of the present invention has substantially vertical side wall portions having a predetermined depth at the end edge portions of the bit fitting groove of the screw head, and non-planar bottom portions raised from the lower edge portion of the vertical side wall portions toward the center portion of the screw head. In addition, inclined groove portions are formed from the raised portion of the non-planar bottom portions toward the center portions of the screw neck. Thus, when the tip of the driver bit engages the bit fitting groove, the tapered contact area of the entire bit fitting groove is partial and small. Furthermore, the non-planar bottom portions is formed in such a way that the area of the side wall portions abutting the tip of the driver bit at the boundary portion between the neighboring bit fitting grooves is enlarged. Thus, the come-out phenomenon of the driver bit is securely prevented. 
     The plus-and-minus screw of the second example of the present invention is a plus-and-minus screw in which a bit fitting groove comprising of a cross groove is formed in the screw head, one of the crossing linear grooves of the bit fitting groove is formed so that a blade of the Phillips® screwdriver bit can fit in and engage the groove, and the other linear groove is formed so that a flat-blade screwdriver bit can fit in and engage the groove. The plus-and-minus screw has the vertical end wall portion having a predetermined depth at the end edge portion of the one linear groove that the blade of a Phillips® screwdriver bit fits in and engage. Thus, the tapered contact area of the one linear groove is made partial and small upon the engagement of the tip of the driver bit with the bit fitting groove. Further, the groove bottom portion of the bit fitting groove is formed so that the area of the side wall portion that the tip of the driver bit abuts is enlarged. Thus, the com-out phenomenon of the driver bit is securely prevented. 
     In addition, in the screw of the first example and the plus-and-minus screw of the second example, the bit fitting groove that the blade of the drive bit fits in and engage is formed as a groove whose width is enlarged little by little from the center portion of the screw head toward the outer portion in the radial direction, so that the opening angle of the opposing side wall portion of the neighboring grooves is a little narrower than 90 degrees. Thus, balanced torque transmission is achieved for the screw fastening operation. In addition, in the combination with a driver bit, the com-out phenomenon from the bit fitting groove of the screw can be prevented effectively. 
     The driver bit adapted to the screw of the first example has a flat blade with a horizontal surface portion at the tip that engages the non-planar bottom portions formed at the end edge portion of the bit fitting groove of the screw, and a protrusion formed on the tip of the blade to be adapted to the shape of the groove portion extending from the non-planar bottom portions. Thus, the most suitable driver bit for the screw can be obtained. 
     Furthermore, the driver bit adapted to the plus-and-minus screw of the second example has flat blades having the substantially horizontal surface portions at the tip engaging the groove bottom portions formed at the end edge portion of the one linear groove of the screw, and protrusions adapted to the shape of the groove portions extending from the groove bottom portions at the end edge portion of the blade. Thus, the most suitable driver bit for the plus-and-minus screw can be obtained. 
     In addition, in the present invention, the screws can be mass-produced easily and in low cost by using the header punch having the protrusions or the protruding lines that are adapted to the shape of the bit fitting groove of the screw and the plus-and-minus screw. 
     Especially, in the forming process of the bit fitting groove of the screw head of the screw and the plus-and-minus screw of the present invention, the non-planar bottom portions raised from the lower edge portion of the vertical end edge portion toward the center of the screw head by using the protrusions or the protruding lines of the header punch. In the mass-production of the screws, even if the protrusions or the protruding lines are worn a little, the forming of the raised non-planar bottom portions is not influenced at all. Thus, the screws and plus-and-minus screws of the present invention can be mass-produced in a low cost. 
     In addition, in the forming process of the bit fitting groove of the screw head in the present invention, the raised portion from the end edge portion of the vertical end wall portion toward the center portion of the screw head can keep the thickness of the screw neck properly, so that the screw having sufficient strength for fastening and loosening can be produced. 
     The screw and the plus-and-minus screw of the present invention has a tapered contact area of the entire bit fitting groove that is basically partial and small upon engagement with the driver bit. In addition, the area of the side wall portion of the bit fitting groove that the tip of the driver bit abuts is enlarged. Therefore, the com-out phenomenon of the driver bit is canceled substantially. This effect is performed also when the conventional drive bit shown in FIG. 31 is used. Therefore, the screw and the plus-and-minus screw of the present invention can achieve correct screw fastening operation even if the driver bit shown in FIG. 31 is used. Especially, in the combination with the screw shown in FIG. 3 or with the plus-and-minus screw shown in FIG. 18, automatic machine can be used in the production line for fastening screws and the screw fastening operation can be achieved smoothly. 
     In addition, according to the screw and the plus-and-minus screw of the present invention, even if the breakage (reference numeral  15 ) shown in FIG. 30 or  34 , for example, in a part of the bit fitting groove of the screw head due to the come-out phenomenon, proper fastening and loosening operation of the screw can be achieved without the come-out phenomenon by using the driver bit of the present invention. 
     In addition, according to the combination of the screw or the plus-and-minus screw and the driver bit of the present invention, even if the bit fitting groove of the screw is blocked with dust or the screw axis and the bit axis are not coaxial, the com-out phenomenon or a breakage of the screw does not occur. Thus, the rotation of the driver bit can be transmitted to the screw smoothly and the normally proper torque is applied so that the screw fastening operation can be achieved quickly. 
     Namely, by using the combination of the screw or the plus-and-minus screw and the driver bit of the present invention, normally proper torque is applied to a hard or soft object that the screw is fastened for secure screw-fastening operation. In addition, the breakage of the screw is reduced substantially, so that the safety of the screw-fastening operation and the working efficiency can be improved easily and economically. 
     In addition, the driver bit for the plus-and-minus screw of, the third example of the present invention is a driver bit for the plus-and-minus screw adapter to plus-and-minus screws having the bit fitting groove formed by a pair of linear grooves consisting of the inclined groove portion and the horizontal groove portion crossing each other at the center portion of the screw head. The drive bit has, the flat blade forming the inclined end edge portion fitting in along the inclined groove portions of the plus-and-minus screw, and the flat blade forming the horizontal end edge portion crossing the flat blade and fitting in along the horizontal groove portions, and extending substantially perpendicular to abut the groove bottom portion of the horizontal groove portion. The tip center portion of each blade is provided with a protrusion fitting in the conical-shaped bottom portion. Thus, in the same way as the other examples, upon the engagement with the screw, the engaging contact area of the side wall portion of the tip portion with the side wall portion of the bit fitting groove is enlarged. Therefore, the come-out phenomenon of the driver bit is prevented so that a proper screw-fastening operation and the screw-loosening operation can be achieved. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only. Thus, it should be understood that the invention is not limited to the illustrative examples in this specification. Rather, the invention is intended to cover all modifications and variations that come within the scope of the following claims and their equivalents. 
     
       
         
               
               
             
           
               
                 APPENDIX E 
               
               
                   
               
               
                 Element 
                 Reference Character 
               
               
                   
               
             
             
               
                 screw 
                 10 
               
               
                 screw head 
                 10a 
               
               
                 screw neck 
                 10b 
               
               
                 grooves 
                 12 
               
               
                 groove portions or grooves 
                 12a, 12b 
               
               
                 tapered wall 
                 13 
               
               
                 bottom surface 
                 14 
               
               
                 hatching portion 
                 15 
               
               
                 connection surfaces 
                 17a, 17b 
               
               
                 driver bit 
                 20 
               
               
                 blades 
                 22 
               
               
                 extension blade 
                 22a 
               
               
                 tapered side walls 
                 23 
               
               
                 screw 
                 30 
               
               
                 screw head 
                 30a 
               
               
                 head portion 
                 30b 
               
               
                 head or top surface 
                 30c 
               
               
                 bit fitting groove 
                 32 
               
               
                 end or lateral wall 
                 32a 
               
               
                 lower edge corner portion 
                 32a′ 
               
               
                 inclined portion 
                 32a″ 
               
               
                 inclined wall bottom portion 
                 32b 
               
               
                 raised or corner portion 
                 32b′ 
               
               
                 inclined groove or wall portion 
                 32c 
               
               
                 tapered portion 
                 32d 
               
               
                 side wall 
                 33 
               
               
                 tapered sidewall portions or grooves 
                 33a, 33b 
               
               
                 opening angle 
                 β 
               
               
                 bottom surface 
                 34 
               
               
                 tapered connection surfaces 
                 37a, 37b 
               
               
                 driver bit 
                 40 
               
               
                 blade 
                 42 
               
               
                 tip surface 
                 42a 
               
               
                 end edge portion 
                 42a′ 
               
               
                 protrusion 
                 42b 
               
               
                 vertical protrusion 
                 42c 
               
               
                 side wall portions 
                 43, 43a, 43b, T1, T2, T3, T3′, T4′ 
               
               
                 torques 
                 0, 1 
               
               
                 Bit axis 
                 L1 
               
               
                 screw axis 
                 L0 
               
               
                 slant angle 
                 θ 
               
               
                 header punch 
                 50 
               
               
                 protrusion 
                 52 
               
               
                 protruding edge portions 
                 52a, 52a″ 
               
               
                 protrusion line 
                 52b 
               
               
                 plus-and-minus screw 
                 60 
               
               
                 screw head 
                 60a 
               
               
                 screw neck 
                 60b 
               
               
                 bit fitting groove 
                 62 
               
               
                 grooves 
                 62a, 62b, 62a′, 62b′ 
               
               
                 end wall portion 
                 63a 
               
               
                 lower edge portion 
                 63a′ 
               
               
                 bottom portion 
                 63b 
               
               
                 groove portion 
                 63c 
               
               
                 bottom surface 
                 64 
               
               
                 side wall portions 
                 65a, 65b 
               
               
                 connection surfaces 
                 67a, 67b 
               
               
                 clearance 
                 δ 
               
               
                 driver bit 
                 70 
               
               
                 blade 
                 72 
               
               
                 horizontal surfaces 
                 73a 
               
               
                 end edge portion 
                 73a′ 
               
               
                 protrusions 
                 73b, 73c 
               
               
                 side wall portions 
                 75, 75a, 75b 
               
               
                 driver bit 
                 80 
               
               
                 blades 
                 82 
               
               
                 end edge portion 
                 83a 
               
               
                 vertical surface portion 
                 83b 
               
               
                 inclined surface portion 
                 83c 
               
               
                 blade 
                 84 
               
               
                 end edge portion 
                 85a 
               
               
                 vertical surface portion 
                 85b 
               
               
                 inclined surface portion 
                 85c 
               
               
                 protrusion 
                 86 
               
               
                 side wall portions 
                 87, 88 
               
               
                 header punch 
                 90 
               
               
                 protrusions 
                 92a, 92b, 93 
               
               
                 inclined protrusion line 
                 93c 
               
               
                 side wall portions 
                 95a, 95b