Inlays require a shallow excavation to seat them flush with the surrounding wood. You can get the job done with other routers too, but a trim router is my first choice. Its small size offers several advantages for precision work like this. Trimmers are much lighter weight than mid-size machines, so you can guide them right up to a knifed outline of your inlay with better control. I use a 1/8″ or 1/4″ straight or spiral bit. If you have a steady hand and a good eye, there’s no need for a template here; just guide the machine freehand. And, if you’re mortising a narrow apron or small box side, a trim router’s little footprint really helps. A few new machines, like RIDGID’s Model R2401, even have an LED light to brighten up the cutting area — and that’s a big bonus for this sort of exacting work.