VizEx Zevo Dual Concentric Stacked Control Knobs are precision-engineered for electric guitars and basses, exclusively fitting metric dual concentric potentiometers with 8mm outer and 6mm inner shafts—NOT compatible with CTS or US-standard potentiometers. The base knob (8mm inner bore) mounts securely on the potentiometer's outer shaft, while the top knob (6mm inner bore) fits the inner shaft, enabling independent dual-function control (volume, tone, etc.) from a single pot to save valuable space on your instrument's control plate. Crafted with knurled metal construction, the non-slip surface delivers a stable hold during play, and tight tolerance precision machining ensures the knobs connect seamlessly with potentiometer shafts for smooth, wobble-free rotation. Each pack includes 2 complete sets of stacked knobs and 1 allen wrench for quick, firm installation—no extra tools needed. Available in classic chrome and black finishes, these knobs complement all electric guitar and bass styles, from vintage to modern builds, making them the ideal upgrade or replacement part for metric potentiometer setups.