The outer diameter measures 50mm ( 46mm inner without adapter), making it space saving yet sturdy for long term use in warehouses or enclosures The 12V18W duct fan delivers powerful airflows with 66m³ / h capacity and 570pa wind pressure, ideal for kitchen, bathroom, pet houses, and 3D printers Features a 5.5X2.1Mm female input ( center positive) for 12V solar panel or adapters for energy option With only 58dB noise levels, this PVC fan ensures quiet while maintaining efficient air circulations For ducts of 50mm / 40mm / 32mm / 25mm / 20mm inner diameters ( optional), offering flexible installation for ventilation needs, Manufacturer: RUINBNC