Dresser Style 39-62 Insulating/Reducing Couplings are most widely used where cast-iron and steel pipe are joined in a system. Plus, it eliminates corrosion problems created when joining pipes of dissimilar metals. The insulating gasket is typically furnished on the larger end for cast-iron. A plastic insulating sleeve prevents pipe-end contact with the middle ring, and a sliding pipe end spacer separates the two pipe ends.