Noctua (NF-S12A PWM) - 120x120x25mm AAO Frame Fan, 4-pin PWM, 1200/900/300rpm SSO2 Bearing, NE-FD1- 2PK Award-winning S12 design: The NF-S12A features the third evolution of Noctuas classic Straight Blade Design that has earned its S12 series countless recommendations from hardware journalists and enthusiasts around the world. Further optimised for even better airflow/noise efficiency, it makes the NF-S12A an ideal quiet case fan. AAO Frame: Integrated anti-vibration pads, Stepped Inlet Design, Inner Surface Microstructures. All further refine the fans performance/noise efficiency. Anti-Stall Knobs: The NF-S12As Anti-Stall Knobs reduce flow separation phenomena in medium to high impedance situations and thereby increase the fans stall margin. This means that the NF-S12A is even more versatile than its renowned predecessor and can achieve better performance on heatsinks and radiators SSO2 Bearing: Provides even better stabilisation, precision and durability Metal bearing shell: a CNC milled bearing shell made entirely from brass provides the highest possible degree of manufacturing precision, minimum tolerance and excellent long-term stability