The stock allowance is relatively minimal on the outside diameter and its primary purpose is to allow for the removal of the roughness of the raw casting. The allowance of the inside diameter is greater to allow for machining to remove oxides and lighter impurities that occur during the casting process. Both allowances vary according to the size of the casting, the thickness of the wall, and the particular alloy that is being used for the end product. The foundry is able to best gauge the proper stock allowance when finished dimensions are given. Call 888-433-3100 to learn more about the process from a centrifugal casting expert.