When sourcing an air pencil grinder, you must prioritize Free Speed (RPM), typically ranging from 56,000 to 70,000 RPM, to ensure smooth finishing. Check the Collet Size, where 1/8" (3mm) is the industry standard, though some precision tasks require 3/32". Additionally, verify the Air Consumption (CFM) to ensure it matches your existing compressor capacity; most high-efficiency models operate at 2-4 CFM at 90 PSI. Look for Twist-Throttle controls for precise speed modulation and integrated silencers to keep noise levels below 80 dB for operator safety.