A pre-rounding element (14) is used in a rounding apparatus (4) for rounding can body blanks from sheet metal blanks. The lower element part (22) of the pre-rounding element (14) is displaceable by an actuation element (23). This allows the adjustment of the pre-rounding element even during operation of the rounding apparatus. Preferably a measurement of sheet metal blank properties takes place. The measurement may include a thickness measurement and/or a strength measurement of blanks. The pre-rounding element is controlled in dependency of the measurement result. This allows a constant rounding result even with varying sheet metal properties.