Guide to Metric Thread Dimensions for Engineers

Threads serve as the foundation of mechanical connections, where precision directly impacts equipment safety and stability. Engineers frequently encounter challenges with mismatched thread dimensions or struggle to locate accurate specifications. This comprehensive reference eliminates those obstacles by detailing ISO metric thread standards.

Metric threads, among the world's most widely used fastener systems, adhere to strict International Organization for Standardization (ISO) specifications. These standards ensure interchangeability between components manufactured globally, facilitating international collaboration. The following table presents critical dimensions for ISO metric coarse threads from M1 through M68.

• Thread Identification: Metric threads begin with "M" followed by the major diameter in millimeters. For example, M6x1 denotes a 6mm major diameter with 1mm pitch.
• Major Diameter: Measures the distance between thread crests, typically verified using calipers or micrometers.
• Minor Diameter: Indicates the distance between thread roots, reflecting load-bearing capacity.
• Pitch: The distance between adjacent thread crests, affecting engagement speed and locking characteristics.
• Tap Drill Size: The pre-threading hole diameter crucial for thread quality and joint strength.
• Clearance Hole: The passage diameter for bolts, typically exceeding the major diameter for assembly tolerance.

These specifications represent theoretical values—actual applications must account for manufacturing tolerances. Material properties and environmental conditions significantly influence threading operations. Engineers should conduct test runs on scrap material before final production and implement rigorous measurement protocols to ensure quality.

For convenient reference, professionals may print this dimensional table for workshop use. Comprehensive understanding of thread parameters enables informed engineering decisions, ultimately enhancing project outcomes.