Hydraulic steel tubes ST37.4 are made in accordance to DIN 2391 / DIN 2445. It also called as seamless precision steel tube. ST37.4 steel tubes have a NBK finishing, where tubes are normalized, phospated, and oiled inside and outside.
Hydraulic tubes ST37.4 are measured by Outer Diameter (OD) and varies tube thickness (THK). Difference of OD and tube thickness will lead to different working pressure.