The roller bearing bases are divided into two types: one is a forging base, and the other is a cast iron (gray iron) bearing base. The forging bases are mostly welded to steel pipes, while the cast iron bearing bases are all extruded onto steel pipes. The features of the forging bases are good sealing and strong overall bearing capacity. The major characteristic of the cast iron bearing bases is high concentricity, but their bearing capacity is lower than that of the forging bases.