When sourcing speed reducers, you must prioritize Torque Capacity, Reduction Ratio, and Efficiency. Ensure the nominal output torque exceeds your application's peak load by at least 20% to prevent mechanical failure. For high-precision tasks, focus on Backlash (measured in arcmin); low-backlash planetary reducers are essential for robotics. Additionally, verify the Input Speed (RPM) compatibility with your motor and the Mounting Configuration (flange, foot, or shaft mount) to ensure seamless integration.