Mortise Compression, Spiral Router Bits Viper - (2 Flute) Solid Carbide - Vortex 3168. Cutting Edge Diameter 9/16 Cutting Edge Length 1 Shank Diameter 1/2 Overall Length 3. Compression spirals designed for mortise cuts or cutting 5/8 or thinner material. Designed with a 1/4 upcut or less preventing chipping or fuzzing on the top and bottom of the material being cut. Mortise Cuts are grooves cut in the material usually at a depth equal to or slightly less than the diameter of the tool.