It is the connecting part between the bottom of the cylinder and the cylinder barrel. Argon arc welding is the best, but the cracked part should be touched deeper before welding, otherwise there will be pores inside. Also, it is best to remove the oil cylinder and pull out the piston rod for welding. Arc is easy to hit the piston rod, and it is easy to burn the seal on the piston at high temperature, and it is not easy to weld with oil in the cylinder.