3/8-16NC H3 3 Flute High Speed Steel Spiral Flute Bottom Tap (1011-8617) ~ High speed steel. ~ Ground from solid. ~ Ground thread. ~ A bottoming tap has 1-2 lead threads ground. They are used for continuing to thread a blind hole close to the bottom of the hole. It's difficult to start threading a hole with this tap. ~ Bottoming taps are not necessarily flat on the bottom, they sometimes have a 60 degree tapered point from the manufacturing process.