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