Screw head and tool for use therewith

Abstract

The invention provides a screw head having a hexalobular slot ( 2 ) in the upper surface of the screw head, an upper peripheral wall ( 9 ) of hexalobular planform extending down into the screw head, the upper peripheral wall ( 9 ) being parallel or near parallel to the axis of the screw, a sloping transition surface ( 15 ) extending downwardly and inwardly with respect to the lower edge of the upper peripheral wall ( 9 ), and a tapered recess ( 11 ) extending downwardly from the lower edge of the sloping transition surface ( 15 ), in which the dimensions of the screw head are such that when the screw head is engaged by a tool ( 6 ) having upper ( 16 ) and lower engagement ( 17 ) sections, the lower engagement section ( 17 ) is tapered, and there is a ‘stick fit’ between the surface of the tapered recess ( 11 ) and the external surface of the lower tapered engagement section ( 17 ), and there is no engagement with the sloping transition surface ( 15 ).

1 . Screw head having a hexalobular slot ( 2 ) in the upper surface of the screw head, an upper peripheral wall ( 9 ) of hexalobular planform extending down into the screw head, the upper peripheral wall ( 9 ) being parallel or near parallel to the axis of the screw (to be desig in  FIG. 2 ), a sloping transition surface ( 15 ) extending downwardly and inwardly with respect to the lower edge of the upper peripheral wall ( 9 ), and a tapered recess ( 11 ) extending downwardly from the lower edge of the sloping transition surface ( 15 ), in which the dimensions of the screw head are such that when the screw head is engaged by a tool ( 6 ) having upper ( 16 ) and lower ( 17 ) engagement sections, the lower engagement section ( 17 ) is tapered, and there is a ‘stick fit’ between the surface of the tapered recess ( 11 ) and the external surface of the lower tapered engagement section ( 17 ), and there is no engagement with the sloping transition surface ( 15 ). 
   
   
       2 . Screw head as claimed in  claim 1 , in which the tapered recess  11  is of circular planform. 
   
   
       3 . Screw head as claimed in  claim 1  or  claim 2 , in which there is a close fit at the upper edge of the upper peripheral wall and a loose fit at the lower edge of the upper peripheral wall ( 9 ) with upper engagement section ( 16 ). 
   
   
       4 . Tool for use with a screw head having a hexalobular slot ( 2 ) in its upper surface, and according to any one of  claims 1  to  3 , in which the tool has upper ( 16 ) and lower ( 17 ) engagement sections, and the lower engagement section ( 17 ) is of smaller diameter is and tapered downwardly with respect to the axis of the screw to which the tool is to engage, in which the upper and lower engagement sections are connected with a transition surface which is tapered with a large angle with respect to the axis of the screw. 
   
   
       5 . Tool as claimed in  claim 4 , in which the upper engagement section ( 16 ) is tapered downwardly at an angle with respect to the axis of a screw to which the tool is to engage. 
   
   
       6 . Tool As claimed in  claim 5 , in which the upper engagement section  16  is tapered at an angle of 0.1 to 5 degrees. 
   
   
       7 . Tool as claimed in  claim 6 , in which the upper engagement section ( 16 ) is tapered at an angle of between 1 and 2 degrees. 
   
   
       8 . System comprising screw head having a hexalobular slot ( 2 ) in its upper surface and a tool ( 6 ) for use with the screw head, in which in a lower engagement section ( 17 ) of the tool, the tool is tapered at the same angle as a recess ( 3 ) in the screw, so that the tool can make a ‘stick fit’ connection with the screw. 
   
   
       9 . System as claimed in  claim 8 , and in which there is a transition zone ( 19 ) between the upper and lower engagement sections of the tool in which the tool makes no contact with the screw. 
   
   
       10 . System as claimed in  claim 8  or  claim 9 , in which in an upper engagement section ( 16 ) of the tool, the tool ( 6 ) is tapered at a sharper angle than a peripheral wall ( 9 ) of the screw.