Abstract: A rotary cutting tool comprises a body having opposite ends and a plurality of diametrally opposed pairs of flutes forming cutting edges extending helically from one end of the body toward the opposite end. All of the cutting edges are circumferentially spaced uniformly from one another at the one end of the body. Each cutting edge of one pair of edges is formed on the same and uniform helix, whereas each cutting edge of another pair of edges is formed on a uniform helix which varies from the cutting end of the body toward the opposite end. The steepness of the helices is such that no flute communicates with any other flute and, at a zone between the ends of the flutes, the cutting edges formed by such flutes again are uniformly circumferentially spaced from one another.