This is how Darton receives the ductile iron sleeves from the foundry. At this point it can become any number of sleeves from LS applications, to sleeves for Pro Stock and Funny Car engines. The sleeve's job is to control wear, heat, provide a platform for lubricity, and contain the combustion process without distortion. Cast iron is typically very inexpensive, breaks in well, and is brittle. The opposite of ductile iron, which is more expensive, very strong, has high elongation (meaning flexibility without breaking), and high surface hardness. Ductile is composed of a nodular structure as opposed to cast iron, which has a more graphite-flake structure.