Woodpeckers aluminum plates are the finest router mountin plates on the market. If you want the ultimate in support, stiffness and flatness, look no further, this is it. These plates are machined from cast jig plate the plate of choice for commercial fixture building and machine shops worldwide. All fetures are milled to exacting tolerances on state of art CNC machines. The plate is anodized to harden the surface and reduce friction. With each Cast Aluminum Router Plate, you also receive (3) TwistLOCK Rings, a brass starting pin, spanner wrench and router mounting screws. The ring opening sizes are 1", 1-3/16" and 2-5/8". The router plate itself has a 3-9/16" opening to fit any commonly available router bit.Dimensions: 9-1/4 x 11-3/4 x 3/8 thick.