Aluminium knobs are used to protect and easily control sound systems or rotary potentiometers. PU interior is useful to avoid damage and maintain for a long time. Great decoration accessory for equipment. These great looking buttons are of high quality and precision made of aluminium alloy. The nubs are knurled all around. These buttons do not have a plastic insert. They are CNC machined from one piece of solid aluminum and have a durable anodized finish.