When sourcing thread plug gauges, the most critical factor is the Accuracy Class (Tolerance). For metric threads, common classes include 6H (standard) or 5H (high precision); for unified threads, Class 2B or 3B are standard. You must also specify the Material, typically GCR15 bearing steel or Tungsten Carbide for high-wear environments, with a surface hardness of at least HRC 58-62. Additionally, ensure the gauge type matches your needs, whether it is a Double-ended (Go/No-Go) or a Single-ended design.