Contains two horizontal rolls, one above the other. In some two-high mills the direction of rolling can be reversed, and these are known as reversing mills; i.e., when a piece has passed through the rolls, the rolls are stopped and then rotated in the opposite direction, thus imposing another pass on the steel, the operation being repeated until the desired reduction is attained. Between passes, adjustment is made to the height of the top roll, and/or the piece is moved sideways by means of manipulators, to be in line with other grooves in the rolls.