| 摘要 |
<p>A screw with a recessed head (3) has a crossing recess (4) formed in a top of the head and consisting of a central region (5) and four grooves (6) extending radially from the central region. Each groove is tapered to reduce width towards an outer conical bottom (9), which defines the groove together with opposite side walls (7, 8) transmitting torque. The bottom connecting outer edges of the side walls has a width 'A' larger than width 'a' in the widely used standard recesses of the same length 'M'. The side walls have a radial length 'B' smaller than 'A', and distance 'C' between the intersections of two side walls of different grooves is equal to or larger than the product of 1.5 and 'A'. One side wall (7) lies in a flat plane in parallel with the screw's axis, and is located forward in a tightening direction of the screw. The conical bottom (9) slanted 5 DEG relative to the axis provides a conical sticking surface. The crossing recess simply modified will transmit a stronger torque and affording a larger sticking area resistant to a stronger thrust, when driven with a driver bit matching the recess. <IMAGE> <IMAGE></p> |
