When sourcing used machinery, you must prioritize the Screw Diameter and L/D Ratio (Length-to-Diameter), as these determine the output capacity and material homogenization quality. Inspect the Screw and Barrel for wear and tear; a clearance exceeding manufacturer limits can reduce efficiency by 20-30%. Additionally, verify the Motor and Drive System type (AC vs. DC) and ensure the Heating Zones and Cooling Systems are fully functional to maintain precise temperature control for specific polymers like PE, PP, or PVC.