... Lift/ Spring 2.Long Span 3.Reliable Quality 4.Five Year Warranty 5.SGS Test, ISO 9000 Certificate, OEM Products NameGas ... Class 1---1.2mm, cheaper price, two year warranty(Normal)Class 2---1.5mm, cheaper price, three year warranty(Better)Class 3---2.0mm, expensive ... price, five year warranty(Much Better)Class 4---2.5mm ...