A billet is a length of metal that has a round or square cross-section, with an area less than 36 in2 (230 cm2). Billets are created directly via continuous casting or extrusion or indirectly via hot rolling an ingot or bloom. Billets are further processed via profile rolling and drawing. Final products include bar stock and wire. Centrifugal casting is also used to produce short circular tubes as billets, usually to achieve a precise metallurgical structure. They are commonly used as cylinder sleeves where the inner and outer diameters are ground and machined to length. Because their size is not modified significantly, they are not always classified as semi-finished casting products.