PTR90 Series 9mm Single Turn Linear Rotary Potentiometer with Rotary Switch PTR90 series 9mm linear rotary potentiometer with rotary switch, a carbon element, an audio taper option and a tracking error within 3 dB. This PTR90 series 9mm potentiometer has a 15mm metal knurled shaft. Typical applications for this PTR90 series linear rotary potentiometer include audio/TV sets, automotive sound systems, amplifiers, mixers, drum machines, synthesizers, DJ equipment, multimedia sound systems and portable electronics.