Main Menu


Request A Quote Contact Us

Your browser is out of date.

You are currently using Internet Explorer 7/8/9, which is not supported by our site. For the best experience, please use one of the latest browsers.

Miniature & Instrument Series Ball Bearings
Ball Bearings

Miniature Ball Bearings 

AST Bearings has a huge selection of miniature ball bearings and instrument series bearings, featuring over 500 types in our product assortment. Precision tolerances from ABEC-1 through ABEC-9 are generally available for most miniature products. 


Miniature ball bearings are generally classified as ball bearings with an outside diameter of 10 mm or smaller. These bearings are often used in high-precision applications such as medical devices, dental handpieces, laboratory devices, drone sensors, kitchen blenders, robotic tools, small hand drills, fluid meters, and rotary encoders. These applications typically involve high-speed, high-load, and heavily constrained operating conditions with the goal of achieving very precise motion/movement. 


Bearings Catalog

Check out our online product catalog with more than 10,000 products with full specifications & 3D CAD Models available for download - all free of charge!

Products are available in the following standard materials (both inch and metric dimensions):

  • 52100 Chrome Steel
  • 4000 Series Stainless Steel
  • ACD34 Stainless Steel
  • SV30 Stainless Steel

Standard Materials - Features and Benefits

Chrome Steel 

  • 52100 chrome steel (or its equivalent) is the most common material used to produce the load-carrying components (inner ring, outer ring, balls) in precision ball bearings.
  • The chemical composition of this steel has a high carbon content and approximately 1.5% chromium content.
  • The finished bearing components have high strength to resist cracking and a hard surface to resist subsurface rolling contact fatigue.
  • The typical surface hardness for bearing components made from this material ranges from 60- 64 on the Rockwell hardness C scale (Rc).

400 Series Stainless Steel 

  • For higher temperature applications and cases where the bearing will be exposed to very humid environments and water, martensitic stainless steel (AISI 440C or equivalent) is a much more suitable bearing material to use than chrome steel.
  • Bearings made from 400 series stainless steel can operate at higher temperatures than 52100 chrome steel, usually up to 250°C continuous.
  • The carbon content in 400 series stainless steel is high enough so it can be hardened using standard heat-treating methods, up to 58 Rc.
  • Due to the decreased hardness limit of this steel, the load carrying capacity of 400 series stainless steels is generally 20% lower than that of 52100 chrome steel bearings.
  • ACD34 is similar to 440C but has slightly lower carbon and chromium content.  This results in smaller carbides after heat treatment, producing a bearing with superior low-noise characteristics while offering the same corrosion resistance as 440C

SV30 Stainless Steel

  • SV30 is a high-strength, high-hardness steel with superior microstructure that extends fatigue life by as much as 100% in certain applications.
  • This material is a modified version of martensitic stainless steel, with a lower carbon content and increased saturation of chromium due to the addition of nitrogen as an alloying element.
  • SV30 also offers enhanced corrosion resistance, up to 5 times better than that of 440C and ACD34.
  • SV30 can be 20-40% higher in cost than other bearing steels, but this premium price is often offset by gains in superior performance of the bearing.


Shielded Bearing – “ZZ” 

  • A shielded bearing is a good choice for high-speed, high-temperature, or torque-sensitive applications.
  • There is no appreciable impact on torque or speed when using shields.  Since no contact exists between the shields and bearing inner ring, bearing rotation of a shielded bearing can be compared to that of an open bearing.

Sealed Bearing – “2RS”

  • A sealed bearing is typically used when the operating environment involves corrosive fluids that can accelerate bearing corrosion and easily wash away the bearing lubricant.
  • A bearing seal is commonly made of Buna-N rubber bonded to a steel insert. The seal is fixed into a groove in the bearing outer ring and the seal lip makes contact on the inner ring.
  • This type of seal can be removed and reused, but care must be taken not to bend the insert or cut the seal lip.

Configurations of AST miniature ball bearings include:

  • Open
  • Open, with extended inner ring
  • Shielded
  • Shielded, with extended inner rings
  • Sealed
  • Sealed, with extended inner rings
  • Flanged, open
  • Flanged, open , with extended inner ring
  • Flanged, shielded
  • Flanged, shielded, with extended inner ring
  • Flanged, sealed
  • Flanged, sealed, with extended inner ring



  • Both petroleum-based and synthetic oils are available for use in bearings.
  • Examples of synthetic oils are silicone, diesters, PAO’s, and fluorinated compounds. Bearings lubricated with oil will exhibit less start-up and running torque and have a higher speed capability than that of greased bearings.
  • Oils are subject to evaporative losses; therefore, the service life in a bearing is less than that of grease.
  • Miniature and instrument bearings are often only lubricated once for the life of the bearing, making the choice of lubricant critical.
  • Temperature range, viscosity, and evaporative rate are key characteristics to consider when selecting an oil.


  • Grease consists of a base oil with an added thickener.

-Thickeners consist primarily of metallic soaps (lithium, sodium, aluminum, and organic or inorganic compounds).

-Thickeners greatly influence the characteristics of a grease, while the lubricating properties of a grease are attributable to its base oil.


  • Grease can contain additives that improve its performance.

-Additive types include antioxidant, anticorrosion, anti-wear, fillers, fortifiers, and extreme pressure fortifiers.


  • Temperature range, base oil viscosity, and stiffness or penetration level are key characteristics to consider when selecting a grease.
  • Most greases used in rolling element bearings are classified as NLGI grade 2.


Instrumentation and Precision Machinery: 

Laboratory equipment, optical devices, and other precision instrumentation may require miniature bearings with very tight tolerances and runout features to achieve accuracy and repeatability.  ABEC 5/P5 precision or higher is commonly recommended for these applications due to the sensitive nature of the equipment design and the precise motion needed during device operation.  Every fraction of an inch in terms of bearing tolerances may considerably influence the ability of an instrument to accurately measure, detect, or scan an object. 

Medical Devices:

Surgical tools and dental drills typically run at very high operating speeds and are subjected to repeated high-temperature and high-pressure cleanings in an autoclave. These devices are supported by miniature bearings designed to meet demanding operating conditions such as high rotating speeds, exposure to steam, and low noise requirements. Important bearing specifications to consider for medical applications are material, precision, radial play, and lubrication. Selecting the most suitable bearings for these applications can significantly improve the operation of medical devices, giving medical professionals more confidence when it comes to providing proper patient care. 


Given the highly demanding operating conditions of a miniature ball bearing, every bearing specification must be given proper consideration to maximize bearing functionality and prevent premature bearing failure in a given application.

Miniature Ball Bearings are small bearings with balls for rolling elements. These bearings typically have an outside diameter of less than 3/8” (<9.525 mm).  A bearing is also considered to be miniature if it has an outside diameter less than or equal to 1/2” (≤ 12.7 mm) with a ratio of outside diameter to inside diameter less than or equal to two.

AST Bearings specializes in miniature, or small, bearings of all types - not limited to "miniature ball bearings" as described in the tab to the left. Often, the label "miniature" is not specified for other small bearing types. If you are looking for small bearings other than miniature ball, you can find them elsewhere on our site in their respective categories including (but not limited to):

Instrument Ball Bearings are not limited to a certain size range, as with miniature ball bearings.  Instrument ball bearings are precision bearings with functional requirements that allow for their use in highly sensitive applications, including metrology, instrumentation, and machine control.   The tolerances of instrument bearings are always ABEC-5 or higher.  Additionally, instrument ball bearings must meet at least two of the following conditions: 

  • Low or uniform starting or running torque.
  • Low vibration levels.
  • A definite contact angle or preload (or both).
  • High cleanliness standards.

Need Assistance Selecting the Proper Miniature & Instrument Series Ball Bearings?

If you need help in selecting the best products for your particular application, please remember that design engineering and application assistance are available from AST as part of our value-added services designed to make your job easier.

Value added services

Ask A Question

Ask us a question and one of our team members will respond as soon as possible.
Fields marked with * are required.