Aluminum knobs are for sound equipments or rotary potentiometer, for protection and easy control. Pu interior is useful to avoid damage and for long time service. great decoration accessory for equipments.hese great looking knobs are high quality and precision machined from an aluminum alloy. The knobs have a knurled finish around their circumference. These knobs do not have a plastic insert; they are CNC machined from one piece of solid aluminum, with a durable anodized surface finish.