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