Spiral scroll saw blades are essentially flat blades twisted into a spiral. Flat blades cut only from the front, but spiral blades cut in every direction—from the front, back, and side to side. This ability is useful for projects that are too long to spin on the saw table without hitting the back of the the saw arm. It is difficult to cut straight lines with these blades. I use them to cut fretwork portraits, which have few straight lines. Using a spiral blade takes practice; they can be difficult to control because they cut everything they touch. The kerf (saw cut) of a spiral blade is wider than the kerf of the same size of flat blade. Spiral blades come in skip-tooth and reverse-tooth configurations.