An apparatus for simultaneously forming a plurality of closely spaced, parallel grooves having a web between them in a thin-walled tube is described. The apparatus includes a tube holding mechanism, a rotating cutting tool and a device for driving the cutting tool. The cutting tool includes a single insert form cutter for forming the grooves. The insert includes a plurality of cutting blades and chip relief members which prevent chips from building up in the tool. The chip relief members are generally triangle-shaped and are disposed on the cutting edge of the insert form cutter.