This operation is done by two grooved rolls. Fig. 68 shows a plan view of this machine with the upper roll removed.

These rolls force the tube over a fixed mandrel A supported between the rolls by a bar B. The bar is supported by a yoke C. Several passes through the rolls over the mandrel A reduce the tube wall to the thickness desired, and give uniform diameters. The size of the mandrel and of the roll passes determine the thickness and diameters of the tube. This operation leaves scratches inside the tube which are removed in the next operation.