Multi-tiered-recess screws

Abstract

A screw ( 10 ) and driver ( 30 ) system comprises a range of screws and a driver. Each screw has a head ( 12 ) having a driving recess ( 14 ) in its surface ( 13 ) for engagement by the driver. Each screw has a longitudinal axis ( 100 ). The recess ( 14 ) of larger screws in the range have a plurality of superimposed recess-tiers ( 16 a,b,c ) of decreasing size with increasing depth from said surface. Each recess-tier has substantially parallel driving surfaces. They are substantially parallel the longitudinal axis. The driver and recess are shaped so that, when the driver is engaged with the recess of any screw in the range, torque applied to the driver is transmitted to the screw through said driving surfaces. At least one recess-tier ( 16 c ) of at least smaller screws in the range has a rib ( 20 ) which is parallel the longitudinal axis ( 100 ) and encroaches into the space of the recess-tier occupied by the driver when it is engaged with the recess. Engagement of the driver with the recess causes deformation of rib, and hence creation of an interference fit of the driver in the recess.

1 . A screw and driver system comprising a range of screws and a driver for said range, each screw comprising a head having a driving recess in its surface for engagement by said driver and a longitudinal axis, in which the recess of larger screws in the range have a plurality of superimposed recess-tiers of decreasing size with increasing depth from said surface, each recess-tier having substantially parallel driving surfaces substantially parallel said longitudinal axis, and in which said driver and recess are shaped so that, when the driver is engaged with the recess of any screw in said range, torque applied to the driver is transmitted to the screw through said driving surfaces; wherein, an interference is provided between the driver and at least one recess-tier causing deformation of the recess when the driver is inserted therein.  
     
     
         2 . A system according to  claim 1 , wherein said interference comprises at least one recess-tier of the screws in said range having a rib parallel said longitudinal axis and encroaching into the space of said recess-tier occupied by said driver when it is engaged with said recess, whereby engagement of the driver with the recess causes deformation of said rib and hence creation of an interference fit of said driver in said recess.  
     
     
         3 . A system according to  claim 1 , wherein each said recess-tier of said screws is a non-circular polygon in section.  
     
     
         4 . A system according to  claim 3 , wherein, in said larger screws, said polygons are concentric.  
     
     
         5 . A system according to  claim 4 , wherein said recess-tiers are the same polygons.  
     
     
         6 . A system according to  claim 5 , wherein said recess-tiers are angularly offset with respect to one another.  
     
     
         7 . A system according to  claim 2 , wherein said rib is in a recess-tier which is common to all screws in the range.  
     
     
         8 . A system according to  claim 2 , wherein said rib is in the single recess-tier of single recess-tier screws, and a different recess-tier in screws having a plurality of recess-tiers.  
     
     
         9 . A system according to  claim 2 , wherein said rib is the full depth of only one recess-tier, where there are multiple recess-tiers, or of the recess-tier, where there is only one recess-tier.  
     
     
         10 . A system according to  claim 2 , wherein said polygonal recess-tiers have flanks, said rib being central in one flank.  
     
     
         11 . A system according to  claim 2 , wherein said polygonal recess-tiers have flanks, the rib being in a corner between two flanks.  
     
     
         12 . A system according to  claim 11 , wherein a rib is provided in each corner between the flanks of the recess-tier.  
     
     
         13 . A system according to  claim 2 , except  claim 8 , wherein it is the smallest recess-tier in each screw of the range that is provided with said rib.  
     
     
         14 . A system according to  claim 1 , wherein the smaller screws in said range have only one recess-tier.  
     
     
         15 . A system according to  claim 1 , wherein said interference comprises at least one tier of the driver having a rib parallel said longitudinal axis, said rib encroaching into the space occupied by the driving surfaces of the corresponding recess-tier of a screw in said range and when the driver is engaged with said recess, whereby engagement of the driver with the recess causes deformation of said driving surface by said rib and hence creation of an interference fit of said driver in said recess.  
     
     
         16 . A system according to  claim 1 , wherein the smallest tier of said driver comprises a distal end thereof and a proximal end, and said interference comprises a tapering of the cross-section of said smallest tier from said proximal to said distal end, the cross section of the tier intermediate said ends corresponding with the cross section of the smallest recess-tier of a screw in said range, whereby, when the driver is engaged with the recess of a screw, the driving surfaces of the smallest recess-tier of the screw are deformed creating an interference fit between them.  
     
     
         17 . A system according to  claim 16 , wherein said tiers and recess-tiers are polygonal in section and concentric, said tapering being around the entire periphery of the tier or recess-tier, as the case may be.  
     
     
         18 . (canceled)  
     
     
         19 . A system according to  claim 1 , wherein the smallest recess-tier of the recess of each screw in said 
 range has a bottom end and an open top end, said interference comprising a tapering of the cross-section of said smallest recess-tier from said open top end to said bottom end, the cross section of the recess-tier intermediate said ends corresponding with the cross section of the smallest tier of said driver.    
     
     
         20 . A system according to  claim 19 , wherein said tiers and recess-tiers are polygonal in section and concentric, said tapering being around the entire periphery of the tier or recess-tier, as the case may be.  
     
     
         21 . A screw for a system according to  claim 1 , which screw includes a recess-tier having said rib.  
     
     
         22 . A screw according to  claim 21 , made by a cold forming process wherein the recess is formed by a punch of corresponding shape to the recess being formed.  
     
     
         23 . A screw according to  claim 22 , wherein said recess rib is formed by a groove formed in the flank of said punch.  
     
     
         24 . A driver for a system according to  claim 15 .  
     
     
         25 . A driver for a system according to  claim 16 .  
     
     
         26 . A screw and driver system comprising a range of screws and a driver for said range, each screw comprising a head having a driving recess in its surface for engagement by said driver and a longitudinal axis, in which the recess of larger screws in the range have a plurality of superimposed recess-tiers of decreasing size with increasing depth from said surface, each recess-tier having substantially parallel driving surfaces substantially parallel said longitudinal axis, and in which said driver and recess are shaped so that, when the driver is engaged with the recess of any screw in said range, torque applied to the driver is transmitted to the screw through said driving surfaces; wherein, an interference is provided between the driver and at least one recess-tier causing deformation of the recess when the driver is inserted therein; wherein the smallest tier of said driver comprises a distal end thereof and a proximal end, and said interference comprises a tapering of the cross-section of said smallest tier from said proximal to said distal end, the cross section of the tier intermediate said ends corresponding with the cross section of the smallest recess-tier of a screw in said range, whereby, when the driver is engaged with the recess of a screw, the driving surfaces of the smallest recess-tier of the screw are deformed creating an interference fit between them.  
     
     
         27 . A driver for the system of  claim 26 , the driver having a longitudinal axis and an end, and a plurality of superimposed tiers of increasing size with increasing distance from said end, each tier having substantially parallel driving surfaces substantially parallel said longitudinal axis, and whereby, when the driver is engaged with the recess of a screw in said range, torque applied to the driver is transmitted to the screw through said driving surfaces, wherein the smallest tier of said driver comprises a distal end thereof and a proximal end, the cross-section of said smallest tier tapering from said proximal to said distal end.  
     
     
         28 . A driver according to  claim 27 , in which said tapering is straight.  
     
     
         29 . A system according to  claim 26 , wherein said tiers are a non-circular polygon in section.  
     
     
         30 . A system according to  claim 29 , wherein said polygons are concentric.  
     
     
         31 . A system according to  claim 29 , wherein said tiers are the same polygons.  
     
     
         32 . A system according to  claim 31 , wherein said tiers are angularly offset with respect to one another.  
     
     
         33 . A screw and driver system comprising a range of screws and a driver for said range, each screw comprising a head having a driving recess in its surface for engagement by said driver and a longitudinal axis, wherein the recess of larger screws in the range have a plurality of superimposed recess-tiers of decreasing size with increasing depth from said surface, each recess-tier being polygonal in section having substantially parallel driving flanks substantially parallel said longitudinal axis, and wherein said driver and recess are shaped so that, when the driver is engaged with the recess of any screw in said range, torque applied to the driver is transmitted to the screw through said driving surfaces; wherein, at least one recess-tier of at least smaller screws in said range has ribs parallel said longitudinal axis disposed in the corners between the flanks of said one recess-tier and encroaching into the space of said recess-tier occupied by said driver when it is engaged with said recess, whereby engagement of the driver with the recess causes deformation of said ribs and hence creation of an interference fit of said driver in said recess.