Bk 5 DIN2391 Steel Seamless Pipe Hydraulic Cylinder Tube DIN2391 Part 2 Specifies dimensions for cold finished, seamless precision steel tubes and is to be used in conjunction with DIN2391 part2 which states the relevant technical delivery conditions.DIN2391 ST52 Honed Pipes and Tubes, EN10305 E355 Hydraulic Bk 5 DIN2391 Steel Seamless Pipe hydraulic cylinder st52 stkm11a seamless tube and pipe