1. The most common method and generally the best conduction of heat from the inside of a cylinder barrel to the cooling air is accomplished by A. machining fins directly on the outside of the barrel. B. shrinking on a jacket or muff of aluminum cooling fins around a steel cylinder sleeve. C. machining fins directly on the outside of the barrel and shrinking on a jacket or muff of aluminum cooling fins around a steel cylinder sleeve (on different areas of the barrel).