When selecting sewing thread, you must prioritize Fiber Type (e.g., 100% Spun Polyester, Core-spun, or High-tenacity Nylon) based on the application. Key metrics include Tensile Strength (Tenacity) to prevent breakage during high-speed sewing, and Elongation at Break to ensure seam elasticity. For industrial use, verify the Resultant Count (Tex or Ticket number) to match the needle size and fabric weight. Additionally, ensure Colorfastness to Washing and Light meets ISO 105 standards to prevent bleeding or fading.