When sourcing a used rolling mill, you must prioritize the mill type (e.g., 2-Hi, 4-Hi, or Universal) and the maximum rolling force. Key parameters include the roll diameter and barrel length, which determine the width and thickness of the steel produced. Additionally, verify the motor power (kW) and drive system efficiency, as these directly impact production speed and energy consumption. Ensure the Automatic Gauge Control (AGC) system is functional or upgradable to maintain precision tolerances.