Unnecessary but I love it. (5V 40mm on 52pi cooler for pi4) : r/Noctua
Noctua NF-A4x10 5V Quiet Cooling Fan 40mm
Noctua NF-A4x10 5V Quiet Cooling Fan 40mm
NF-A4x10 5V
Noctua expands 5V fan line-up
NF-A4x20 5V PWM
High Quality Noctua NF A4x10 FLX 40mm 12V 5V 40X40X10 Cooling Fan 4010 Silent Cooler Fan Radiator 3D Printer Parts for ENDER 3|3D Printer Parts & Accessories| - AliExpress
Noctua A4x20 PWM 5.53 CFM 40 mm Fan (NF-A4x20 PWM) - PCPartPicker