Insert rings that closely encircle your router bit help to control dust and provide more flat reference surface around the bit for clean, accurate cuts. These are made from sturdy, transparent ABS plastic for good visibility while routing freehand. A range of inside diameters—1-1/4'', 1-1/2'' and 2-1/2''—are included to fit various router bit sizes. The 1-1/4'' ring has the required recess to mount standard guide bushings.