Abstract: An attachment for power tool such as a router adapted to cut an end of circular cross-section onto a rectangular piece of wood suitable for use as a circular tenon in mortise and tenon construction, the attachment being formed from a block of solid material adapted to be attached to the power tool adjacent the cutting element thereof, said block of solid material having a recess therein with a solid pointed metal element such as a drill bit centered in said recession, attached to the bottom thereof and protruding therefrom to form a point upon which the wood to be cut can be rotated, there being a groove or cut-away portion in said block adjacent and extending into a side of said recession to receive the cutting element of the tool.