Seamless steel tubes are a type of welded steel tube, referring to tubes where the weld is parallel to the longitudinal axis of the tube. They are categorized by wall thickness into thin-walled seamless tubes and thick-walled seamless tubes; by shape into round tubes, square tubes, or other-shaped tubes; and by application into general-purpose welded tubes, galvanized welded tubes, oxygen-welded tubes, wire sleeve tubes, metric welded tubes, roller tubes, deep well pump tubes, automotive tubes, transformer tubes, electric welding thin-walled tubes, electric welding non-standard tubes, and spiral-welded tubes.