When evaluating hand grinding machines (angle grinders), you must prioritize motor power (wattage), typically ranging from 800W to 2500W depending on the workload. Ensure the no-load speed (RPM) aligns with your material; for instance, stainless steel requires variable speed control to prevent overheating. Check for brushless motor technology, which offers longer service life and higher efficiency compared to traditional carbon brush motors. Additionally, verify the disc diameter compatibility (common sizes: 100mm, 115mm, 125mm, or 180mm) to ensure it fits your specific application needs.