This two flute spiral bit is designed for solid woods, wood composites and some plastics. A down-cut spiral bit is used where a downward chip removal and a good finish on top are required. A down-cut spiral bit provides downward pressure on the material and leaves an excellent finish on the top. Always refer to the operation manual of your router first, in the event that a router bit doesnt come with a speed chart, you may start at about 2,000 rpm slower than the maximum speed described in the chart below. Maximum speed below is for reference only, actual best performance speed varies depending on a number of factors i.e. size of the router bit, the material to be cut, etc. Run 24,000 rpm maximum for 1" overall diameter router bits; Run 20,000 rpm maximum for 1-1/2" overall diameter router bits; Run 18,000 rpm maximum for 2" overall diameter; Run 16,000 rpm maximum for 2-1/2" overall diameter router bits; Run 12,000 rpm maximum for 3" overall diameter router bits; Run 10,000 rpm maximum for 3-1/2" overall diameter router bits;