A bulk 5-liter (1.32 gal) barrel of REED's ultrasonic couplant gel for high-volume thickness-gauging work on iron, steel, aluminum and titanium. Water-soluble with good transducer lubrication and a thick, slow-drying consistency (roughly 80,000 cP) that holds on overhead and vertical surfaces, it's rated for use from about -10 to 210F (-23 to 99C) and suits shops running the R7900-series or similar ultrasonic thickness gauges regularly.