Spiral router cutter HS with base blade

Spiral groove cutters in HS steel, 6 to 20 mm on an 8 mm shank. The spiral flute lifts chips up and out of the cut, so the groove stays clear and the extractor gets the waste instead of the cutter re-cutting it. HS steel is ground for softwood, where it runs particularly smoothly. Deeper grooves are where the spiral earns its keep — a straight cutter packs solid.