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 (16a,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 (16c) 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.

Abstract: A screw and driver system includes a range of screws and a driver. Each screw has a head having a driving recess in its surface for engagement by the driver. 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 tier has substantially parallel driving surfaces and torque applied to the driver is transmitted to the screw through the driving surfaces. At least one tier of at least smaller screws in the range has a rib. Engagement of the driver with the recess causes deformation of rib, and hence creation of an interference fit of the driver in the recess.