Aluminum flat bar size: 1/4″ Thickness X 1″ Width X 12″ Length, 6mm X 25mm X 305mm. Aluminum flat bar size: 1/4″ Thickness X 1″ Width X 12″ Length, 6mm X 25mm X 305mm. -Aluminium flat bar is widely used in machinery parts, precision machining, trucks, trams, furniture and DIY craft making projects, ect.