Wine for shipping and transport is usually packed in wooden crates, more rarely in strong cardboard boxes. The internationally customary quantity for crates is 12 bottles of 0.75 litres. This quantity is due to the fact that it can be carried comfortably by one person. The wine bottles are packed lying in the crate. If production quantities are indicated in "crates", this refers almost exclusively to crates with 12 bottles. Wines intended for longer bottle aging are packed in sturdy crates made of mostly spruce wood. Wines offered in unopened crates are considered particularly valuable in the special trade. They are labelled OHK = Original Wooden Case (OWC = Original Wooden Case, in French CBO = Caisse en Bois Original). A case with six bottles of two different types or four bottles of three different types is called a "split case", a case with twelve different types is called a "mixed case". It is also common to find packaging in cartons of six bottles, although these are usually upright.