Beyond the Jargon: Understanding Basic Dimensions and Dimensional Tolerances in Rolling Bearings

Beyond the Jargon: Understanding Basic Dimensions and Dimensional Tolerances in Rolling Bearings

When selecting and installing rolling bearings, two technical terms often appear on engineering drawings: Basic Dimension and Dimensional Tolerance. They may sound like specialist jargon, but understanding them is essential for achieving precise assembly, ensuring stable operation, and extending bearing service life.

What is the Basic Dimension?

The Basic Dimension is the theoretical size specified on a mechanical design drawing—essentially the “ideal” size for a part. In rolling bearings, this includes:

• Inner Diameter (d): The maximum radial dimension of the bearing’s inner ring. For deep groove ball bearings, the inner diameter code × 5 = actual inner diameter (when ≥ 20 mm; e.g., code 04 means d = 20 mm). Sizes below 20 mm follow fixed codes (e.g., code 00 = 10 mm). Inner diameter directly affects the radial load capacity.

• Outer Diameter (D): The minimum radial dimension of the outer ring, influencing load capacity and installation space.

• Width (B): For radial bearings, width impacts load capacity and rigidity.

• Height (T): For thrust bearings, height influences load capacity and torque resistance.

• Chamfer (r): A small curved or beveled edge that ensures safe installation and prevents stress concentration.

These theoretical values are the design starting point. However, due to manufacturing processes, perfect accuracy is nearly impossible to achieve—and that’s where tolerances come in.

What is Dimensional Tolerance?

Dimensional Tolerance is the allowable deviation in bearing size and rotation accuracy from the basic dimension during actual manufacturing.

Formula: Dimensional tolerance = Upper deviation – Lower deviation

Example: If a bearing bore is 50.00 mm with an allowable range of +0.02 mm / −0.01 mm, the tolerance is 0.03 mm.

Tolerances are defined by precision grades. Higher grades mean stricter tolerances.

International Standards for Bearing Tolerances

ISO Standard Grades:

• P0 (Normal): Standard precision for general industrial use.

• P6: Higher precision for high-speed or medium-load applications.

• P5 / P4: High precision for machine tool spindles or precision machinery.

• P2: Ultra-high precision for instruments and aerospace applications.

ABEC (ABMA) Grades:

• ABEC 1 / 3: Automotive and general industrial use.

• ABEC 5 / 7 / 9: High-speed, high-precision applications such as CNC spindles and aerospace instruments.

Why This Matters for Your Business

Choosing the right basic dimension and tolerance grade is critical to ensuring optimal bearing performance, avoiding premature wear, and preventing costly downtime. The correct combination ensures:

• Perfect fit with shafts and housings

• Stable high-speed performance

• Reduced vibration and noise

• Longer service life

TP – Your Reliable Bearing Manufacturing Partner

At Trans Power (www.tp-sh.com), we are a manufacturer with over 25 years of experience producing rolling bearings, wheel hub units, and custom bearing solutions.

• Strict ISO & ABEC compliance – All our bearings are manufactured and tested to meet or exceed international standards.

• Full range of precision grades – From P0 for general use to P2 for ultra-precision applications.

• Custom engineering support – We can produce non-standard dimensions and special tolerance levels to fit your exact application.

• Global supply capability – Factories in China and Thailand, serving customers in 50+ countries.

Whether you need bearings for general industrial equipment, high-speed machinery, or aerospace-level precision, TP delivers quality you can trust.

Enhance your equipment’s reliability.
Optimize performance with the right dimensions and tolerances.
Partner with a proven global bearing manufacturer.

Contact TP today to discuss your requirements, request samples, or get a free technical consultation.
 Email: info@tp-sh.com |  Website: www.tp-sh.com