Copper coolers of a special design were developed by the companies Mechel and Mi-Fi-Bu in 2002. A distinctive feature of the Mechel/Mi-Fi-Bu coolers is the presence of three water inlets in the lower part of the cooler and three outlets in the upper part. A standard cooler has three pairs of drilled channels (for inlet and outlet tubes). Projections are welded on the outside surface of the body of the cooler at the same locations as the bolts to maintain the required gap between the cooler and the shell of the blast furnace.