Low Helix, Downcut, Finisher, Spiral Router Bits - (2 Flute) Solid Carbide - Vortex 4350. Cutting Edge Diameter 1/2 Cutting Edge Length 1 1/4 Shank Diameter 1/2 Overall Length 3 1/2. Our double edge low helix spiral bits are recommended for cutting hard plastics, such as acrylic and phenolics. The lower helix angle produces less lifting and fluttering of the plastic material. Tools are extremely sharp producing very clean edges on plastic materials requiring little secondary work. These bits also provide great finishes in hardwoods.