Fastener and driver assembly

Claim 1

A fastener and driver combination comprising: a fastener having a recessed drive socket, said socket including a center axis and being multilobular in cross-section and having an inner surface formed by alternating and smoothly joined flutes and lobes which extend longitudinally, and essentially parallel to said socket center axis; and a driver for imparting rotational torque to said fastener and including a driving head portion having a tip end and a center axis, said driving head portion having an outer surface portion, including a plurality of axially extending flutes and lobes sized for mating engagement with the corresponding flutes and lobes of said drive socket, said driving head portion in cross-section being multi-lobular with the outer surface portion thereof comprising a first set of concaved, longitudinally extending curved surfaces and a second set of longitudinally extending convexed curved surfaces, said first and second sets of curved surfaces alternating and merging smoothly to define said plurality of axially extending flutes and lobes, with the apecies of said convexed curved surfaces defining longitudinally extending crests portions for said lobes, and the apecies of said concaved curved surfaces defining longitudinally extending trough portions for said lobes and only one of said first or second sets of curved surfaces and the crest or trough portions defined thereby being axially parallel to said center axis of said driving head portion, while the other said set of curved surfaces and the crest or trough portions defined thereby being tapered axially, such that said last mentioned tapered crest or trough portions converge in a direction toward said tip end to enable said driving head portion to enter said fastener drive socket to a predetermined depth with interferring engagement being attained only between said axially tapered crest or trough portions and the set of mating surfaces of said socket, thereby to control and insure the desired depth of engagement of said driver head portion in said drive socket while attaining a friction fit between said fastener and said driver which serves to maintain said fastener mounted on the end of said driver.