Ideal for USA made electric guitar/bass/amplifier/effect pedal etc. Inch size, fine 24 splines, will fit most American made 6mm(15/64 inch) split shaft potentiometers like CTS/Fender/DiMarzio/Bourns, will NOT fit metric size potentiometers like Alpha Inner hole diameter: 6mm(15/64 inch), height: 16mm (5/8 inch), base outer diameter: 29mm(1-9/64 inch) Made of ABS plastic, aluminum top reflector