The POWERTEC 71218 2-1/2" Router sub base for Porter cable 690 and 890 Series routers helps you get your router jobs that require a larger sized bit done to perfection. With it larger 2-1/2 inch center hole you can use a much wider variety of bit sizes, instead of being limited to only those bits that are 1-3/16" In diameter or smaller. To install, simply use the included mounting screws, and easily attach to your router. Bring your router up to its full potential with this handy, durable accessory; now you can use all your bits!