SILENT WINGS PRO 4 140mm PWM LEGENDARY SILENCE, EPIC PERFORMANCE AND FEATURES Silent Wings Pro 4 140mm PWM is the most progressive, performant and versatile fan by be quiet! Optimized fan blades for the highest performance on radiators and heat sinks Speed switch allows changing maximum PWM speed between medium-speed, high-speed and ultra-high-speed (up to 2400 rpm) Small tip clearance and a fan frame with a funnel-shaped air outlet for extremely high air pressure Virtually inaudible operation at regular speed 6-pole fan motor and fluid-dynamic bearing for less vibration and very smooth operations Individual mounting systems for use as a case fan or with a radiator