Dedicated push-pull set (Sx2-PP) with two round-frame NF-A14x25r G2 PWM 140x25mm fans that are slightly off-set in speed (+/- ~25rpm) in order to avoid undesired acoustic interaction phenomena State-of-the-art engineering (Progressive-Bend impeller with winglets and Centrifugal Turbulator, Flow Acceleration Channels, AAO frame) and construction (Sterrox LCP, ultra-tight tip clearance) Ideal choice for push-pull applications on 14cm CPU coolers such as the NH-D15, NH-D15S or NH-U14S series, next-generation quiet cooling performance with unprecedented acoustic fine-tuning measures Includes anti-vibration mounts, fan screws, Low-Noise Adaptors (LNA), extension cables and y-cable for running two fans on the same header Trusted Noctua quality with premium-grade SSO2 bearing (MTTF > 150,000 h), safety certifications from UL and TÜV, protected against reverse polarity, over voltage and over current (short-circuits)