Holediameter

Holediameter, commonly referred to as hole diameter, is the internal diameter of a hole or bore in a component. It defines the opening through which a shaft, fastener, or other part passes and is a critical dimension for mating parts. The term applies to through holes that extend completely through a part as well as blind holes that terminate within the material.

Measuring holediameter involves determining the distance across the hole along its axis at a specified depth. Tools used include inside calipers or micrometers, bore gauges, plug gauges, and coordinate measuring machines. In manufacturing, hole size is controlled through a sequence of operations such as drilling, reaming, or boring, often finished with honing or grinding for tighter tolerances. The measurement depth, orientation, and surface condition can affect the effective size.

Standard tolerances for holes are part of a system of limits and fits, described in standards such as ISO 286. Hole tolerances are expressed with a letter that denotes the tolerance zone relative to the basic size; for example, H indicates a zero lower deviation (the hole may only be larger than or equal to the basic size). The combination of hole and shaft tolerances determines whether a clearance, interference, or transition fit results with a mating part. Actual values depend on nominal size and the chosen tolerance class (for example H7, H8, etc.).

Applications of hole diameters span mechanical assemblies, such as locating dowel pins, mounting flanges, or allowing fasteners to pass through. Accurate hole sizes are essential for alignment, function, and structural integrity. Quality control often uses go/no-go gauges or CMM measurements to verify that the hole diameter falls within specified limits.