Tap

Claim 1

A tap comprising a shank having a tapping section and a drive tool-engaging section, said sections having a common longitudinal axis, said tapping section having a work-entering end portion and an adjacent working portion, said working portion being axially intermediate said end portion and said drive-tool engaging section, said tapping section also having a continuous roll-type thread in said end portion and in said working portion, the thread on said end portion and said working portion having a cross section of arcuate, polygonal lobular configuration with an odd number of arcuate sides and intermediate circumferentially spaced arcuate lobes, the lobes in the work-entering end portion defining a series of progressive thread-swaging surfaces of increasing radius from said axis, the drive tool-engaging section also having a cross section of arcuate polygonal lobular configuration and which in geometrically similar to said cross section in said working portion and with the corresponding lobes and arcuate sides of the two last-mentioned cross sections being respectively parallel and coaxial, whereby the arcuate sides of the tool-engaging section may be gripped by a drive tool chuck or the like so that the axis of rotation of said chuck coincides with said common axis to provide concentric gripping of the tool over a substantial length of the tap; the tap, prior to the formation of the thread thereon, being a blank which in cross section is of arcuate polygonal lobular configuration that is geometrically similar to said cross section in said drive toolengaging section.