I have posted a variation somewhere here before, but i will freshen it up for this thread. Its for "square" edged Dominos going into a round mortise in drawer sides.
What I do. Make my own out of some contrasting timber, I make 5mm for small drawers and 6mm for large drawers (because the 6mm cutter does not have the flare-out and you can go deeper into the sides for a stronger bond.
After i have glued and clamped the rebated drawer and its dry, I then plunge the Domino mortise to full depth according to the cutter used.
Example - If you plunge 28mm (Red line on the Domino) then cut your home made Domies around 32- 35mm lengths (Yellow line) Scribe a line all round 25mm up from the bottom (Blue line) and with sharp chisel, from the blue scribe line back down to the bottom, round over the edges to fit in the mortise. The 3mm left above the scribe (between Red and Blue) remains square, and that will force a square edge into the top of the round mortise, giving the illusion of a hand mortised joint.
Two tips -
1- On the rounded sides (green) chisel them round in both sides an extra 1.5mm, and just before you are going to fit them into the drawer mortise, put the Domi into an engineers vice (about 3 or 4 mm below the blue line) and give it a ¼ turn to slightly compress it. As it compresses for easy fit into the mortise, the sides expand slightly in width, that’s why you remove the 1.5mm from each side so it won’t get stuck.
2- Dont forget to put a clamp either side of the drawer where the mortises are, so when you tap in the Dominos the drawer sides dont split. This is a must because if it splits its easy to glue, but the glue line sticks out and looks terrible.
It looks so much better than a rounded machined Domi look. You still get a slight round if you look close, but its a great illusion for the casual observer for not much extra effort.