Seamless steel pipe with small outer diameter can be called small-diameter seamless steel pipe. Small-diameter seamless steel pipe can also be divided into: 

seamless small-diameter steel pipe and straight seam (also called welding) small-diameter seamless steel pipe. In the outer diameter of the steel pipe of 89 

mm or less, 4 mm or more, the general size is 1/2", 3/4", 1", 1 1/4", 1 1/2", 2", 2 1/2", 3", 3 1/2" can be collectively referred to as small diameter seamless steel tubes.

If you want to obtain a smaller size and better quality seamless pipe, you must use cold rolling cold drawing or a combination of the two. Cold rolling is usually 

carried out on a two-roll mill. The steel pipe is in a circular cross-section with a variable cross section and a fixed cone. Rolling in the shape of an annular hole 

composed of a shaped head, which is usually extruded on a single-chain or double-chain cold drawing machine. The tube blank to be heated is placed in a closed

 extrusion cylinder. The rods move together to extrude the extrusion from the smaller orifice, which produces a smaller diameter steel tube.