With the NA-FK1 second fan set, the NH-U12S redux can be operated in a dual fan configuration. Push/pull setup allows for even higher cooling performance and even lower noise levels when both fans are running at a lower speed. The upgrade kit includes a second NF-P12 redux-1700 PWM fan, fan clamps, anti-vibration pads, a 4-pin PWM Y cable and two low-noise adapters-everything you need to make your NH-U12S redux even more efficient!