It is standard pruoduct the standard is JB/ZQ4181-1997.This series belongs to heavy-duty hydraulic cylinder. Which is specitically designed for metallurgy & heavy-dutymachinery.Because of their functional reliability, good impact and pollution resistance , they  apply to high-temperature , high-pressure and rugged environment.Nowadays.They widely used in metallurgy , roll, ship, aerospace, transport and power equipment.