US Patent 7255522 Spiral drive fastener with engagement ramp

The fastener of this application is designed to facilitate the insertion of rotating power driven tools into the fastener recess. The recess of this fastener generally uses spirally configured driving surfaces and is formed in a counterbore in the upper surface of the fastener. The driving lobes have upper surfaces that are depressed a distance into the counterbore. A ramp surface is formed on each of the upper surfaces that causes a spinning bit to fall into the recess in an engaged manner. The ramp surfaces are constructed with both removal and installation ramp portions.