C250K 20mmx6mm Potentiometer
Understanding the Specifications

• C Taper (Reverse Logarithmic / Audio): The prefix letter "C" represents a reverse logarithmic taper. Unlike common A (audio/log) or B (linear) pots, a C-taper potentiometer changes resistance slowly at the beginning of its rotation and much faster toward the end, but in a mirror image of a standard audio pot. It is most frequently used for specialized audio blending, left-handed guitar volume/tone modifications, or specific electronic timing controls. 
• 250K Resistance: A value of 250kΩ is the standard benchmark for single-coil guitar pickups (like Stratocasters or Telecasters) because it bleeds off a small amount of high frequencies to keep the single-coils from sounding overly harsh or piercing. 
• 20mm x 6mm Physical Sizing:
  • 20mm Length: This typically measures the total length of the actuator shaft (sometimes including the threaded bushing or starting right from it, depending on the manufacturer). A 20mm shaft is perfect for standard panel mounting or thick guitar wood cavities.
  • 6mm Diameter: The 6mm shaft diameter represents the metric standard. Knobs designed for standard US/Imperial pots (which use a 1/4" or 6.35mm shaft) will fit loosely or wobble on a 6mm metric shaft, so ensure your control knobs are rated for 6mm metric sizing.