Made me Think! In the early 60s the US was teaching the metric system in school thinking we should go along with the rest of the world, I loved It! The adult population couldn't shift over so it's not used much, a little but not much. Ok, 3mm is about 1/8, I think.Our wood is milled to ASE, not sure how it's done in the rest of the World? You want to come close to doubling the thickness of the stock doublers is all. Our ply also has several different grades. What we call aircraft is a top grade with 5 or 6 layers. Someone else can tell you what type of wood is used, I can't remember. We also have light ply, three layers of softer wood. Use the really good ply, Aircraft!
Karol once sent me a conversion chart, it's in my saved files, well worth Downloading! It converts almost everything.
it's in my old lap top though, it completely crashed.