When sourcing silver refills (commonly used for marking leather, fabric, or rubber), you must prioritize ink viscosity and line consistency. Ensure the refill uses non-toxic, mercury-free silver ink that provides high visibility on dark surfaces. For industrial applications, verify the ball-point diameter (typically 0.8mm to 1.2mm) to ensure it matches your marking precision requirements. Additionally, check the shelf life, as high-quality silver refills should remain functional for at least 12 to 24 months without drying out.