Overhang trim bits are used immediately after the sink or bowl is mounted, before the final flush trim pass is made. They remove the bulk of the excess material around the opening, leaving approximately 1/8" for the finishing bit to clean up. The router bearing follows the contour of the sink or bowl during this pass, carefully trimming the overhang to shape. Using an overhang bit before the final flush trim extends the life of the finishing bit and improves overall cut quality, as the flush trim bit is only removing a small amount of material rather than doing all the heavy work.