Some of the wooden flasks I have made to accommodate the various part sizes required for the lathe build. What is a flask? Well it basically holds the molding sand in place and gives support when the molding sand is rammed up around the part. Flasks can be 1, 2 or more parts though all of mine are 2 parts. Typically there is a parting line at the middle of the flask and each part needs to have proper draft such that the part can be removed from the sand at that parting line without disturbing the cavity that is left behind when the pattern is removed.