The Amana 55400 cuts material perfectly for fitted tongue-and-groove joints on stock between 3/8" and 1-1/8" thick with a table-mounted router. The tool consists of an arbor with an integral shank, two identical, removable slotting cutters, and a pair of bearings.

To cut tongues, sandwich one bearing between the two cutters.

To cut slots, mount one cutter between the two bearings.