Spiral cutterhead, helical cutterheads are different terminologies that people to name the cutter heads with segmented reversible knives. We call this type helical cutterheads to differentiate it from the spiral cutterheads with curved edge knives.
The edges of the carbide knives are parallel to the centerline of the cutterhead, or straight to the feeding of the board. Even though it does not slice or mill board as the spiral type cuts, the segmented knife edges divide the contact of the full length of the conventional long blade. It cuts smoother and quieter than the cutterhead with long HSS blades does.