Tongue and groove joints have been used to strengthen panels since the dawn of woodworking. Using a matched set of router bits is the easy way to make one that fits. This set made in the U.S.A. by Whiteside works on material from 1/2" to 1-1/4” thick. These cutters are only available in 1/2" shank and should be used in a router table. It's also recommended that you use a fence, aligned flush with the ball bearing for the smoothest, gap free joint. If guiding strictly with the ball bearing, any edge imperfections will telegraph to the joint. A fence will smooth out the travel over those imperfections.