September 16,2026
A common scenario in custom bearing projects: an engineer sends a message asking for a quotation on a custom bearing, and the reply comes back with a list of questions. Bore size? Outside diameter? Load? Speed? Temperature? The engineer thinks, "I just need a bearing that fits." The supplier thinks, "I cannot quote what I cannot define."
This gap between what the customer provides and what the supplier needs is one of the most common causes of delay in custom bearing projects. It is not a matter of unwillingness on either side. It is a matter of missing technical inputs.
This article explains what information is actually needed to design a custom bearing, why each item matters, and how to prepare a custom bearing RFQ that allows a supplier to respond quickly and accurately.
Selecting a standard bearing is largely a matching exercise. Load rating, speed limit, and dimensions are published. The engineer checks whether the catalog product fits the application.
Designing a custom bearing is different. There is no catalog entry to compare against. The bearing must be engineered around the application, which means the supplier must understand the conditions that determine internal geometry, material, clearance, lubrication, and sealing.
Because of this, custom bearing design requirements are broader than standard selection data. The following five categories cover the information most custom bearing projects require.
Start with the space the bearing must occupy: bore diameter, outside diameter, width or height, and any axial or radial space constraints. If the bearing must fit an existing housing or shaft, these dimensions are fixed. If the surrounding design is still flexible, indicate which dimensions can be adjusted.
The interface determines fit, clearance, and mounting method: shaft material and hardness, housing material, fit requirements, mounting method, and shaft or housing deflection under load. Shaft hardness in particular affects wear resistance and is often specified in custom bearing design.
Load determines the bearing type, size, and internal geometry. Provide radial load (continuous and peak), axial load (continuous and peak), direction of load relative to rotation, and any shock or impact loads. Understating peak load is one of the most common causes of premature failure in custom designs.
Speed affects cage design, lubrication, internal clearance, and heat generation. Provide continuous operating speed, maximum speed, and speed variation or duty cycle. For high-speed bearing design, the DN value (bore diameter × RPM) provides a useful initial reference. Final evaluation also depends on bearing type, cage design, lubrication, clearance, preload, and heat dissipation.
Not all bearings rotate continuously. Motion type affects internal design: continuous rotation, oscillating motion, linear motion, indexing, or static load. Oscillating applications may favor a full-complement or specially configured bearing when speed is limited and load capacity is prioritized. Continuous rotation commonly uses a caged design to control rolling-element spacing and friction, particularly as speed increases.
Temperature influences material, lubricant, clearance, and seal selection. Provide normal operating temperature, minimum and maximum temperature, temperature cycling frequency, and nearby heat sources. A bearing that performs well at 20°C may behave very differently at 200°C or at cryogenic temperatures.
Lubrication is often the deciding factor in custom bearing design. Specify grease, oil, or dry lubrication; continuous or intermittent lubrication; possibility of oil starvation or dry running; and any vacuum or cleanroom restrictions. In applications where lubrication cannot be maintained, solid lubricants or ceramic hybrid designs may be required.
The environment determines material and sealing requirements: humidity or washdown, chemicals or solvents, dust or abrasive particles, vacuum or controlled atmosphere, and salt or marine exposure. Environment is one of the most common reasons a standard bearing fails and a custom design becomes necessary.
Precision affects manufacturing cost and lead time. Specify any existing tolerance, runout, dimensional accuracy, or repeatability requirements. If you do not have a defined precision class, the supplier can help determine an appropriate level based on the application.
For medical, instrumentation, and precision motor applications, provide acceptable noise level, vibration class (V1–V4), noise class (Z1–Z4), and acoustic testing requirements. These requirements influence raceway finish, ball grade, lubricant selection, and inspection procedures.
In motor or generator applications, specify whether electrical insulation is required, bearing current risk, and conductivity requirements. Electrical insulation is typically addressed with ceramic rolling elements or ceramic-coated rings.
If the custom bearing replaces an existing one, provide the OEM part number, technical drawing, physical sample, dimensional measurements, and failure history. In many cases, an existing sample or OEM part number is enough to begin an initial feasibility review, even without a complete drawing.
You do not need a complete specification to start a custom bearing discussion. If an existing bearing is no longer available, reverse engineering from a sample is often the starting point. For new designs, operating conditions may be estimated and refined during development. The goal of the first request is not to deliver a final specification—it is to give the supplier enough information to assess feasibility and define the next step.
A practical way to organize a request:
Identify the application – equipment type, function, and duty cycle
Provide fixed constraints – dimensions, mounting, interface
Describe operating conditions – load, speed, temperature, environment
State performance requirements – life, precision, noise, electrical insulation
Attach what is available – drawing, part number, photo, sample
Note what is uncertain – indicate which values are estimates
For purchasing teams, it is also useful to state the expected annual quantity, target application, required delivery schedule, and whether the bearing is for prototype, replacement, or series production.
Once the information is received, a typical custom bearing development process follows:
Application review → Feasibility assessment → Design proposal → Prototype and validation → Production
MTWB supports custom bearing development for both replacement and new OEM applications, and can identify any missing information before quotation or prototyping.
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