Abstract: A mandrel mill hydraulic screwdown control was successfully established at Wakayama Steel Works of Sumitomo Metal Industries, Ltd, in 1985. The control is used to preform tube ends into a thinwalled taper during rolling. By preforming the tube ends, it is possible to avoid the end thickening and reduce crop loss in the stretch reducer. The variations in inter-stand tensions when the above-said end thinning control is carried out are analysed and a method for roll speed control to prevent these variations is discussed. The causes of the wall eccentricity and its countermeasures as well as the effects of the end thinning control are covered.