Metric Tolerance Chart

The team at Boston Centerless want to ensure our customers have the resources and data they need to make informed decisions regarding materials acquisition. For this reason, we provide a variety of tools such as the Metric Tolerance Chart below.

The chart below provides ISO 286-2 Round Bar Tolerances. The tolerances are provided for various sizes of round bar within the “h series”.   Our customers can utilize this chart to specify the desired requirements for their precision round bar that enable Boston Centerless to precision grind the bar with the necessary tolerances.

It is important to understand ISO 286-2 in order to properly design, machine, and assemble parts. ISO 286-2 is an international standard that defines tolerance grades for round bar and establishes tolerances for how much bar can deviate from its nominal dimension and still be able to fit within a given hole. The key benefit of utilizing ISO 286-2 is that standardization eliminates confusion and ambiguities regarding tolerances, ensuring design and machining alignment across all parties. Additionally, the use of ISO 286-2 ensures components will mate properly regardless of the manufacturer or country, allowing for interchangeability of parts.

ISO 286-2 specifies various alphabetical tolerance grades, or series, that vary in the degree of exact fit. The Metric Tolerance Chart below is for the H Series, which is known for delivering a precise fit. Further, ISO 286-2 provides a range of fits for round bar: clearance, interference, and transition. Clearance fits are more loose, interference fits are tighter, and transition fits are in the middle. The fit for precision round bar is defined numerically, ranging from H5 to H12 in the Metric Tolerance Chart below.

Use this chart to determine what the round bar tolerance is in millimeters and inches based on the diameter.
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