1.It is divided into drill string crossover and tubing Crossover. 2.Drill string Cross-over is divided into type A, type B and type C. Crossover subs are made from AISI41455H chrome molybdenum alloy steel, and the content of micro-element can be controlled availably. The surface of sub threads are phosphated or copperized. According to shapes and applications, crossover subs are divided into three types: Type a stands for the same diameter: one crossover sub has one size. Type b stands for reduce type: one crossover sub has two sizes. Type c for left hand thread type: the connection thread is left hand type. Use: it plays a role of connectivity and conversion in different specifications drilling tools. Characters: crossover subs are complied with SY5200-93 or API Spec7. All products must be ultrasonic nondestructive tested and the surface copper coated. Crossover subs of various types and lengths are available.