Noctua (NF-A15 PWM - 140x150x25mm Round Frame Fan, 4-pin PWM, 1200/900rpm max - 2pk Round Frame w/150mm width: Tailor-made for use on today's high-end CPU coolers: While its 150mm width matches those of most high-end heatsinks, its 140mm height doesn't make it extend on top and thus ensures best case compatibility. Standard 120mm mounting holes (105mm spacing) also make it an ideal performance upgrade for 120mm case or CPU fans. AAO Frame: Integrated anti-vibration pads, Stepped Inlet Design, Inner Surface Microstructures. All further refine the fan's performance/noise efficiency. Flow Acceleration Channels: Leads to better efficiency and lower vortex noise. 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