How to Select Fit Tolerances for Bearing Installation? Should the Inner Ring with Shaft, and Outer Ring with Bearing Housing Use Interference Fit or Clearance Fit?

Core Principles for Fit Selection

Fit tolerance selection depends on load direction, rotational state of bearing rings, and service conditions (e.g., temperature, precision requirements).

The key rule: The ring that rotates with the load should use an interference fit; the stationary ring can use a clearance fit or transition fit.

Fit for Inner Ring & Shaft

Priority choice: Interference fit (e.g., H7/k6, H7/m6 for medium loads; H7/n6 for heavy loads or high precision).

Reasons: The inner ring typically rotates with the shaft and bears radial loads. An interference fit prevents relative slipping (skidding) between the inner ring and shaft, avoiding wear or damage to the shaft surface.

Exception: For light loads, low speeds, or scenarios requiring easy disassembly, a transition fit (e.g., H7/h6) can be used.

Fit for Outer Ring & Bearing Housing

Priority choice: Clearance fit (e.g., H7/j6, H7/h7) or loose transition fit.

Reasons: The outer ring is usually stationary relative to the bearing housing. A clearance fit allows the bearing to expand freely with temperature rises during operation, avoiding internal stress that could affect rotation precision or damage the bearing.

Exception: If the outer ring needs to rotate (e.g., some special transmission structures), an interference fit should be used for the outer ring, while the inner ring adopts a clearance/transition fit.

Supplementary Notes

For high-precision equipment (e.g., machine tools), tighter tolerance grades (e.g., IT5-IT6) are recommended to ensure rotation accuracy.

For applications with large temperature variations, the fit should be adjusted appropriately-increase clearance for high-temperature environments to compensate for thermal expansion.