ISO 286-1/2 – Limits and Fits Chart (H7/g6)

Explore ISO 286 limits and fits chart (H7/g6). Quickly find hole and shaft tolerances for proper mechanical fits and assembly performance.

Overview of ISO 286-1/2

ISO 286 defines the system of limits and fits used to control the clearance or interference between mating parts such as holes and shafts. It standardizes tolerance grades (IT grades) and fundamental deviations (letters like H, g, etc.) to ensure consistent fit selection.

ISO 286-1 covers the general system and definitions, while ISO 286-2 provides the tables of standard tolerance grades and deviations. Together, they are essential for mechanical designers working with precision assemblies and functional fits.

Limits and Fits Chart (Common Fits)

Hole Basis System (Most Common)

Fit Type

Example

Description

Use Case

Clearance Fit

H7/g6

Always leaves space between parts

Used for sliding or rotating parts

Transition Fit

H7/k6

May result in slight clearance or interference

Used for precise alignment components

Interference Fit

H7/p6

Parts are forced together

Used for permanent or high-strength assemblies

Fit Classes Overview

Fit Category

Description

Clearance

Shaft is always smaller than the hole

Transition

May result in either clearance or interference

Interference

Shaft is always larger than the hole

Core Concepts

Limits and Fits

Technical Product Specification (TPS)

Defines the relationship between hole and shaft sizes to control assembly behavior.

Purpose: Ensures correct function, motion, or rigidity between parts.

Defines the relationship between hole and shaft sizes to control assembly behavior.

Purpose: Ensures correct function, motion, or rigidity between parts.

Tolerance Grades (IT Grades)

ISO GPS Integration

Numerical system (e.g., IT6, IT7) defining the precision level of a dimension.

Purpose: Controls how tight or loose a tolerance is.

Numerical system (e.g., IT6, IT7) defining the precision level of a dimension.

Purpose: Controls how tight or loose a tolerance is.

Fundamental Deviations

Model-Based Definition (MBD)

Letter-based system (e.g., H, g, h) defining the position of the tolerance zone relative to the nominal size.

Purpose: Determines whether a fit results in clearance or interference.

Letter-based system (e.g., H, g, h) defining the position of the tolerance zone relative to the nominal size.

Purpose: Determines whether a fit results in clearance or interference.

High-Cost Errors

Incorrect fit selection can lead to assembly failure, wear, or excessive manufacturing costs.

Choosing the Wrong Fit Type

Using clearance instead of interference (or vice versa) can cause loose assemblies or failure under load.

Ignoring Tolerance Stack-Up

Overlooking how tolerances combine across parts leads to unexpected fit issues during assembly.

Failing to apply linked ISO standards results in incomplete or incorrect specifications.

How to Apply ISO 286

Define Functional Requirement

Determine whether the fit requires clearance, transition, or interference.

Select Fit Type

Choose a standard combination (e.g., H7/g6).

Identify Tolerance Grades

Select appropriate IT grades based on required precision.

Reference ISO Tables

Use ISO 286-2 tables to find exact limits and deviations.

Validate Assembly Fit

Ensure the selected fit works under real operating conditions.

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Comparison & Related Standards

ISO 286

A detailed system for defining limits and fits between holes and shafts in precision engineering.

ISO 2768

A general tolerance standard used when individual tolerances are not specified.

ISO 1101

Defines geometrical tolerancing used alongside limits and fits.

ISO 8015

Establishes the independency principle across ISO standards.