Flush-Trim Router Bit

A flush-trim bit pairs a straight cutting edge with a guide bearing of the same diameter, mounted either above or below the cutting edge. Run against a template or pattern clamped to a rough-cut workpiece, the bearing rides the template's edge while the cutter trims the workpiece flush to match it exactly -- the standard way to produce multiple identical parts from one master template, or to clean up a bandsawn curve to a precisely drawn line.

Top-bearing and bottom-bearing versions exist so the template can be positioned on whichever side of the workpiece is more convenient for a given setup, and pattern bits (a close relative with the bearing mounted on the bit's shank rather than at the cutting edge) let the template ride on top with the workpiece underneath, useful when the template itself needs to stay visible during the cut.