Seamless tubes are made by rolling a preheated billet between offset rolls to create a tube shell. The tube shell is then elongated in a multi-stand rolling mill (with a mandrel) to achieve the desired wall thickness and a limited range of diameters. Tube diameter can also be achieved with a sizing collar, but for significant diameter changes the tube is reheated and passed through a stretch-reducing mill a multi-stand mill that reduces outside diameter but not wall thickness. The seamless range also includes Oil Country Tubular Goods (OCTG.)
Boiler tubing, the oil and gas industries and automotive transmission components are typical applications.