Solid shaft means that the axis is not notched but smooth. "A" means it is a logarithmic knob and "B" means "linear". For B, the midpoint is in the middle (!) of the race because it is linear. For A's, the midpoint will not be in the middle because it follows the curve logarithmic. But apart from that, the A's and the B's are identical and interchangeable. are almost all equipped only with linear CTS potentiometers. 500K knobs are generally for humbuckers (humbuckers). The 100k for basses or some rare guitars. But everything is possible, it is a matter of taste, equipment (amp, pedal, pickups) and... ear, so originality, don't hesitate to innovate! The mini knobs (14mm base) are of identical quality to the basic 24mm knobs and can be used as a priority to save space, particularly for bas.
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