Product Description Speed control knob is compatible with electric guitar bass. There are 16 grooved thick (18 tooth splined) shafts on the potentiometer. Easy to install.A good replacement part for broken or old one. Cylinder Style Material:Acrylic Size:As the picture show Colors: Purple Number Color:White or Black Split Shaft:6mm(about 0.24 inch) Package Content:4 Knobs Note: Please allow a little size error due to manual measurement. Please be reminded that due to lighting effects and monitor's brightness/contrast settings etc, the item's color may be slightly different from the pictures.  Please understand.Thanks!