CMT 800.626.11 - 2-Piece TONGUE and GROOVE ROUTER BIT SET - 1/2-inch Shank Make tongue and groove joints without the complicated process of taking apart and reassembling bits. This set gives you one bit to groove the slot and a separate bit to mill the tongue. Or use your imagination and put them to work individually on other projects. They make tongue and groove cuts in wood up to 19mm (3/4”) thick.