Style 39 Insulating Couplings are widely used on gas service lines, but are ideal for water lines, tank hook-ups, intake and discharge lines, pumping stations, at river crossings and on bridge lines where electrical isolation is required. Dresser insulating couplings are effective for insulating hot water heaters as well as other installations. The Style 39 coupling follows the same basic design as the Style 38 coupling, but has insulating properties.