We play a lot of Mexican Train dominoes. While organizing and setting up your train it's really easy to knock them over so a holder is a great help. This will of course work for any domino game so it's a very useful accessory.
Measure the width of 4 of your dominoes the long way. For my set this comes out to 200mm.
Measure the thickness of your dominoes. Mine are around 8mm so a 10mm spacing should work for me.
These sizes are from a pretty standard domino set but double check yours to be sure.
Make a rectangle that is 200mm wide by 110mm (4 dominoes wide and the domino spacing x 11).
Make another rectangle that is 200mm wide by 10mm tall for the spacers. You will need 6 copies of this one.
Cut the parts out. The backer can be cut from 6mm or 3mm, either is fine.
The spacers should be cut once from 6mm OR twice from 3mm and laminate 2 together for the proper thickness. You'll want the spacers to be tall enough to hold your dominoes upright.
In either case, I use the default settings in XCS for these materials
Glue the tile spacers to the backer.
Start by gluing the first one at the far edge. Use another piece as a spacer (no glue) and use it to accurately place the next one (glue this one). Remove the spacer piece. Repeat until only the last piece is left and glue it to the outer edge of the base plate.
Paint if desired and it's game time!