This series of cylinders consists of 14 bore diameters and 28 specifications of single-piston double-acting differential cylinders according to four speed ratios. In addition, the cylinder head flange type, middle trunnion installation type and base installation type can also be made into double-piston rod double-acting constant-velocity cylinders, plus no end buffer and both ends with buffer and the above 28 specifications to form 384 species. It is especially suitable for harsh environments and heavy-duty working conditions.