Gray Beard didn't give away his secret of where he gets those plywood spacer washers from but I'll take a guess.....get out a hole saw with an I.D. about the size you need for a spacer washer O.D. and after cutting a hole in the plywood, you clean out the "scrap" that is left stuck inside the hole saw, sand the edges a little to clean them up and there is your plywood spacer washer. Don't tell G.B. I gave his secret out!