Abstract: A threading tap, having the usual longitudinally extending flutes to provide lands therebetween. Each land is provided with screw-cutting teeth, and each land has at least one cross-groove formed therein of a length equal to at least two teeth and of a depth greater than the root depth of adjoining teeth. A cross-groove in one land is longitudinally off-set from a cross-groove in an adjoining land to provide for chip clearance and yet not materially weaken the structure of the tap.