When designing bolted assemblies, confidence in determining hole tolerances are crucial for ensuring both assembly feasibility and structural integrity.

This guide will walk through the key concepts and calculations needed to determine appropriate hole tolerances.

Why Proper Hole Tolerances Matters

Understanding and correctly specifying hole tolerances is essential for:

• Ensuring ease of assembly in production
• Maintaining structural integrity of the joint
• Preventing costly rework or scrap
• Meeting design requirements for alignment and fit

Key Components

• Master Pin/Hole: The primary reference pin/hole. This pin/hole establishes the baseline for the tolerance calculations.
• Secondary Pin/Hole: The subsequent pin/hole in the components that must align with the master hole to allow assembly.
• Minimum Clearance: The critical space required between the bolt and hole surfaces to enable proper assembly. This value must always be equal to or greater than zero to prevent interference.

The relationship between these components can be expressed as:

Minimum Clearance = Minimum Hole Diameter – Maximum Bolt Diameter

This ensures that even in worst-case tolerance stack-ups, the assembly will still be possible without forcing or damaging components.

Metric Through Hole

Imperial Through Hole