For fast and accurate dadoes, this jig is hard to beat. The trick is to run the router against one guide, then back against the other. This allows you to use a 1/2-in. bit, for example, to cut a dado that's 13/16-in. wide or less, to get a perfect fit with plywood. Because the dado is cut in the end of the jig, you can simply line up the jig with one mark. This makes it hard to goof up by having the dado on the wrong side of the mark. For greatest accuracy, make a dedicated jig to fit one router and one bit. Note: The jig will only cut one size dado.