When it comes to machinery, bearing specifications might seem like a small detail, but they play a massive role in keeping operations running smoothly. From precision ball bearings in high-speed motors to heavy-duty industrial components in mining or construction equipment, dimensions directly affect performance, fit, and longevity.
But if you’ve ever looked at a spec sheet filled with dimensions like “25mm x 52mm x 15mm” or seen codes like “6205-2RS,” you know the sizing system can be confusing.
- What exactly do those numbers represent? How are they measured?
- And more importantly, how do you choose the right measurements for your application?
In this guide, we’ll break down how industrial components are sized, why there are so many variations, and how to make confident decisions when selecting or replacing them. You’ll also find helpful measurement tips, sizing charts, and expert insight from the team at Central Surplus – your go-to partner for high-quality, in-stock bearings and MRO parts at competitive prices.
Whether you’re a sourcing specialist, a repair technician, or an engineer, this article will help you make smarter decisions about dimensions, diameter ranges, materials, and more.
How are Bearings Sized & Why So Many Measurements?
Bearings are measured based on three core dimensions usually measured in millimeters (mm):
- inner diameter (ID)
- outer diameter (OD)
- width (W)
These values correspond to how the unit fits within a shaft and housing, directly influencing its load capacity, speed rating, and ability to support rotational motion under varying levels of friction and pressure.
For example, a ball bearing listed as “25mm x 52mm x 15mm” means:
- 25mm inner diameter (bore size)
- 52mm outer diameter
- 15mm width
This system is part of what’s called the boundary dimensions, a universal standard that allows engineers and procurement professionals to find interchangeable options across brands and series.
But why are there so many sizes?
It’s because each application has its own mechanical requirements: different shaft diameters, speed limits, axial and radial loads, temperature ranges, and equipment configurations. The right dimensions help:
- Reduce friction between moving parts
- Provide stability under dynamic or static loads
- Enable smooth operation with minimal wear
- Handle precise clearances for high-speed or high-heat environments
Industries like automotive, machinery, manufacturing, and food processing all use bearings, but the requirements vary wildly. This drives the need for a broad range of sizes and styles, from ultra-small miniature components to large, heavy-duty roller bearings used in mining conveyors.
And while precision matters, availability does too. That’s why working with a supplier like Central Surplus, which offers thousands of products in stock across different diameters and boundary dimensions, can save your team both time and money.
How Do You Measure Ball Bearings? (It’s Simpler Than You Might Think)
If you’re trying to find a replacement and don’t have a part number, measuring the bearing manually is the next best step. It’s a straightforward process that requires only a digital caliper or a micrometer.
Here’s the three things to look for:
- Inner Diameter (ID) – Also called the bore diameter, this is the measurement of the hole in the center. It should match the shaft size the bearing is intended to mount on.
- Outer Diameter (OD) – This is the total width from one outside edge of the bearing to the opposite edge. It must match the housing bore.
- Width (W) – Also called thickness or height, this is the distance between the two flat faces of the bearing.
These three boundary dimensions (ID, OD, and W) are critical to ensure the part will fit and perform as intended.
Where to Go for Reliable Bearings? Rapid Delivery & Expert Service
When time is critical, and you’re unsure of the exact size or part number, Central Surplus makes it simple. With thousands of in-stock parts across nearly every major size series, we help you avoid the long lead times and inflated prices that plague traditional sourcing channels.
Whether you’re replacing a worn-out component or trying to identify a rare industrial series, our team can help you measure, cross-reference, and source what you need quickly. You can even shop directly through our eBay store for a fast, frictionless experience – no complicated portals or forms required.
Need help matching a measurement to the right part? Simply reach out and send us the dimensions or a photo, and we’ll do the rest.
Uncover the Meaning of Bearing Sizes, Classes & Ratings (& How They’re Used)
When selecting a bearing, it’s not enough to simply match the bore diameter or part number; you need to understand how the part performs under real-world conditions. The following charts, drawn from industry reference standards, provide three crucial types of information: dimensions, internal clearance classes, and load ratings.
Above each chart below, you’ll find definitions for the terms so you can navigate them with clarity and confidence.
You can also use these charts to cross-reference series based on fitment requirements, friction limits, or upgrade needs. If you’re not sure what series you need, we can help you compare bearing types based on measured dimensions or application data.
1. Bearing Size Chart – Dimensional Definitions
- Bearing Number: A unique alphanumeric identifier that specifies the bearing’s type, series, size, internal construction, and sometimes special features like sealing or clearance.
- Bore (d) : The inside diameter of the bearing. This must match the shaft the bearing will mount on.
- Outer Diameter (D) : The external diameter of the bearing, which should match the housing bore where the bearing is installed.
- Width (B) : The total width of the bearing, accounting for both inner and outer raceways in a complete unit (primarily used for ball or roller bearings).
- Cone Width (B) : The width of the inner race (cone) component in a tapered roller bearing, excluding the outer cup.
- Cup Width (C) : The width of the outer race (cup) in a tapered roller bearing. Used when components are sold or specified separately.
| 6000 Series (Extra Light) | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 607 | 7 | 19 | 6 |
| 608 | 8 | 22 | 7 |
| 609 | 9 | 24 | 7 |
| 6000 | 10 | 26 | 8 |
| 6001 | 12 | 28 | 8 |
| 6002 | 15 | 32 | 9 |
| 6003 | 17 | 35 | 10 |
| 6004 | 20 | 42 | 12 |
| 6005 | 25 | 47 | 12 |
| 6006 | 30 | 55 | 13 |
| 6007 | 35 | 62 | 14 |
| 6008 | 40 | 68 | 15 |
| 6009 | 45 | 75 | 16 |
| 6010 | 50 | 80 | 16 |
| 6200 Series (Light) | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 623 | 3 | 10 | 4 |
| 624 | 4 | 13 | 5 |
| 625 | 5 | 16 | 5 |
| 626 | 6 | 19 | 6 |
| 627 | 7 | 22 | 7 |
| 628 | 8 | 24 | 8 |
| 629 | 9 | 26 | 8 |
| 6200 | 10 | 30 | 9 |
| 6201 | 12 | 32 | 10 |
| 6202 | 15 | 35 | 11 |
| 6203 | 17 | 40 | 12 |
| 6204 | 20 | 47 | 14 |
| 6205 | 25 | 52 | 15 |
| 6206 | 30 | 62 | 16 |
| 6207 | 35 | 72 | 17 |
| 6208 | 40 | 80 | 18 |
| 6209 | 45 | 85 | 19 |
| 6210 | 50 | 90 | 20 |
| 6300 Series (Medium) | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 6300 | 10 | 35 | 11 |
| 6301 | 12 | 37 | 12 |
| 6302 | 15 | 42 | 13 |
| 6303 | 17 | 47 | 14 |
| 6304 | 20 | 52 | 15 |
| 6305 | 25 | 62 | 17 |
| 6306 | 30 | 72 | 19 |
| 6307 | 35 | 80 | 21 |
| 6308 | 40 | 90 | 23 |
| 6309 | 45 | 100 | 25 |
| 6310 | 50 | 110 | 27 |
| NU 2xx Series | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| NU 203 | |||
| NU 204 | 20 | 47 | 14 |
| NU 205 | 25 | 52 | 15 |
| NU 206 | 30 | 62 | 16 |
| NU 207 | 35 | 72 | 17 |
| NU 208 | 40 | 80 | 18 |
| NU 209 | 45 | 85 | 19 |
| NU 210 | 50 | 90 | 20 |
| NU 211 | 55 | 100 | 21 |
| NU 212 | 60 | 110 | 22 |
| NU 3xx Series | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| NU 304 | 20 | 52 | 15 |
| NU 305 | 25 | 62 | 17 |
| NU 306 | 30 | 72 | 19 |
| NU 307 | 35 | 80 | 21 |
| NU 308 | 40 | 90 | 23 |
| NU 309 | 45 | 100 | 25 |
| NU 310 | 50 | 110 | 27 |
| NU 311 | 55 | 120 | 29 |
| NU 312 | 60 | 130 | 31 |
| 222xx Series | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 22205 | 25 | 52 | 18 |
| 22206 | 30 | 62 | 20 |
| 22207 | 35 | 72 | 23 |
| 22208 | 40 | 80 | 23 |
| 22209 | 45 | 85 | 23 |
| 22210 | 50 | 90 | 23 |
| 22211 | 55 | 100 | 25 |
| 22212 | 60 | 110 | 28 |
| 22213 | 65 | 120 | 31 |
| 22214 | 70 | 125 | 31 |
| 22215 | 75 | 130 | 31 |
| 22216 | 80 | 140 | 33 |
| 22217 | 85 | 150 | 36 |
| 22218 | 90 | 160 | 40 |
| 22220 | 100 | 180 | 46 |
| 22xx Series | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 2200 | 10 | 30 | 14 |
| 2201 | 12 | 32 | 14 |
| 2202 | 15 | 35 | 14 |
| 2203 | 17 | 40 | 16 |
| 2204 | 20 | 47 | 18 |
| 2205 | 25 | 52 | 18 |
| 2206 | 30 | 62 | 20 |
| 2207 | 35 | 72 | 23 |
| 2208 | 40 | 80 | 23 |
| 302xx Series | |||||
|---|---|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (T) (mm) | Cone Width (B) (mm) | Cup Width (C) (mm) |
| 30203 | 17 | 40 | 13.25 | 12 | 11 |
| 30204 | 20 | 47 | 15.25 | 14 | 12 |
| 30205 | 25 | 52 | 16.25 | 15 | 13 |
| 30206 | 30 | 62 | 17.25 | 16 | 13 |
| 30207 | 35 | 72 | 18.25 | 17 | 14 |
| 30208 | 40 | 80 | 19.75 | 18 | 15 |
| 30209 | 45 | 85 | 20.75 | 19 | 16 |
| 30210 | 50 | 90 | 21.75 | 20 | 17 |
| 12xx Series (Example) | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 1200 | 10 | 30 | 9 |
| 1201 | 12 | 32 | 10 |
| 1202 | 15 | 35 | 11 |
| 1203 | 17 | 40 | 12 |
| 1204 | 20 | 47 | 14 |
| 1205 | 25 | 52 | 15 |
| 1206 | 30 | 62 | 16 |
| 1207 | 35 | 72 | 17 |
| 1208 | 40 | 80 | 18 |
| 72xx Series | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 7200 | 10 | 30 | 9 |
| 7201 | 12 | 32 | 10 |
| 7202 | 15 | 35 | 11 |
| 7203 | 17 | 40 | 12 |
| 7204 | 20 | 47 | 14 |
| 7205 | 25 | 52 | 15 |
| 7206 | 30 | 62 | 16 |
| 7207 | 35 | 72 | 17 |
| 7208 | 40 | 80 | 18 |
| 7209 | 45 | 85 | 19 |
| 7210 | 50 | 90 | 20 |
| 73xx Series | |||
|---|---|---|---|
| Bearing Number | Bore (d) (mm) | Outer Dia. (D) (mm) | Width (B) (mm) |
| 7300 | 10 | 35 | 11 |
| 7301 | 12 | 37 | 12 |
| 7302 | 15 | 42 | 13 |
| 7303 | 17 | 47 | 14 |
| 7304 | 20 | 52 | 15 |
| 7305 | 25 | 62 | 17 |
| 7306 | 30 | 72 | 19 |
| 7307 | 35 | 80 | 21 |
| 7308 | 40 | 90 | 23 |
| 7309 | 45 | 100 | 25 |
| 7310 | 50 | 110 | 27 |
2. Clearance Class Chart – Internal Fit Definitions
- CN or C0 (Normal): The standard internal clearance used in general-purpose applications. This value is typically unmarked.
- C2: Less clearance than Normal. Ideal for precision fits or low-thermal-expansion setups.
- C3: Greater clearance than Normal. Commonly used in applications that involve tight press fits or high operating temperatures.
- C4: Even more clearance than C3. Used in specialized environments where heat or load expansion is extreme.
- C5: Maximum clearance, used in rare or highly specialized engineering scenarios.
| Bore Dia. Over (mm) | Bore Dia. Incl. (mm) | CN Min (µm) | CN Max (µm) | C3 Min (µm) | C3 Max (µm) |
|---|---|---|---|---|---|
| - | 10 | 2 | 13 | 8 | 23 |
| 10 | 18 | 3 | 18 | 11 | 25 |
| 18 | 24 | 5 | 20 | 13 | 28 |
| 24 | 30 | 5 | 20 | 13 | 28 |
| 30 | 40 | 6 | 20 | 15 | 33 |
| 40 | 50 | 6 | 23 | 18 | 36 |
| 50 | 65 | 8 | 28 | 23 | 43 |
| 65 | 80 | 10 | 30 | 25 | 51 |
| 80 | 100 | 12 | 36 | 30 | 58 |
| 100 | 120 | 15 | 41 | 36 | 66 |
| Bore Dia. Over (mm) | Bore Dia. Incl. (mm) | CN Min (µm) | CN Max (µm) | C3 Min (µm) | C3 Max (µm) |
|---|---|---|---|---|---|
| - | 30 | 25 | 40 | 40 | 55 |
| 30 | 40 | 30 | 45 | 45 | 60 |
| 40 | 50 | 35 | 55 | 55 | 75 |
| 50 | 65 | 40 | 65 | 65 | 90 |
| 65 | 80 | 50 | 80 | 80 | 110 |
| 80 | 100 | 60 | 100 | 100 | 135 |
| 100 | 120 | 75 | 120 | 120 | 160 |
| 120 | 140 | 95 | 145 | 145 | 190 |
| 140 | 160 | 110 | 170 | 170 | 0 |
| 160 | 180 | 120 | 180 | 180 | 0 |
| Bore Dia. Over (mm) | Bore Dia. Incl. (mm) | CN Min (µm) | CN Max (µm) | C3 Min (µm) | C3 Max (µm) |
|---|---|---|---|---|---|
| 18 | 24 | 20 | 35 | 35 | 45 |
| 24 | 30 | 25 | 40 | 40 | 55 |
| 30 | 40 | 30 | 45 | 45 | 60 |
| 40 | 50 | 35 | 55 | 55 | 75 |
| 50 | 65 | 40 | 65 | 65 | 90 |
| 65 | 80 | 50 | 80 | 80 | 110 |
| 80 | 100 | 60 | 100 | 100 | 135 |
| 100 | 120 | 75 | 120 | 120 | 160 |
| 120 | 140 | 95 | 145 | 145 | 190 |
| 140 | 160 | 110 | 170 | 170 | 0 |
3. Load Rating Chart – Capacity & Life Definitions
- Dynamic Load Rating (Cr): Indicates the radial load a bearing can withstand for 1 million revolutions without experiencing fatigue damage. Essential for estimating service life under rotating load conditions.
- Static Load Rating (C0r): Defines the maximum load that can be applied to a stationary bearing without causing permanent deformation. Crucial for slow or shock-load scenarios, such as pivot points or parked machinery.
- Limiting Speed (Grease): The highest speed at which the bearing can operate when lubricated with grease, without compromising performance or safety.
- Limiting Speed (Oil): A higher threshold for rotation speed when the bearing is lubricated with oil, due to its superior heat dissipation properties.
| Bearing Number | Bore (d) (mm) | Dynamic Load (Cr) (kN) | Static Load (C0r) (kN) |
|---|---|---|---|
| 6200 | 10 | 5.4 | 2.36 |
| 6201 | 12 | 6.8 | 3.05 |
| 6202 | 15 | 7.8 | 3.75 |
| 6203 | 17 | 9.56 | 4.75 |
| 6204 | 20 | 12.8 | 6.55 |
| 6205 | 25 | 14 | 7.8 |
| 6206 | 30 | 19.5 | 11.2 |
| 6207 | 35 | 25.7 | 15.3 |
| 6208 | 40 | 29.1 | 19 |
| 6209 | 45 | 33.2 | 23.2 |
| 6210 | 50 | 35.1 | 27 |
| Bearing Number | Bore (d) (mm) | Dynamic Load (Cr) (kN) | Static Load (C0r) (kN) |
|---|---|---|---|
| NU 204 | 20 | 25.7 | 22.6 |
| NU 205 | 25 | 32.5 | 29 |
| NU 206 | 30 | 43 | 40.5 |
| NU 207 | 35 | 53 | 52 |
| NU 208 | 40 | 62 | 62 |
| NU 209 | 45 | 70.5 | 72 |
| NU 210 | 50 | 86.5 | 86.5 |
| NU 211 | 55 | 108 | 106 |
| NU 212 | 60 | 112 | 116 |
| Bearing Number | Bore (d) (mm) | Dynamic Load (Cr) (kN) | Static Load (C0r) (kN) |
|---|---|---|---|
| 22208 | 40 | 81.9 | 75 |
| 22210 | 50 | 114 | 104 |
| 22212 | 60 | 143 | 143 |
| 22214 | 70 | 183 | 186 |
| 22216 | 80 | 216 | 240 |
| 22218 | 90 | 291 | 315 |
| 22220 | 100 | 341 | 380 |
| 22222 | 110 | 432 | 490 |
Answers to Your 5 Toughest Bearing Size Questions
When it comes to specifying or replacing these parts, it’s easy to get lost in a sea of dimensions, codes, and compatibility concerns. Whether you’re an engineer verifying fitment or a purchasing agent trying to interpret part numbers, understanding the nuances of sizing standards is crucial.
Below are answers to some of the most commonly asked questions we hear from our customers about measurements, conversions, and substitutions.
1. How are bearing sizes measured?
Bearings are typically measured using three primary metrics: the inner diameter (ID), outer diameter (OD), and width (W). The inner diameter corresponds to the shaft size the bearing will fit onto. The outer diameter aligns with the housing or bore the part fits into, and the width refers to the overall thickness of the unit.
These dimensions are most commonly expressed in millimeters, though inch-based (imperial) sizes exist – especially in North American markets. For precision applications, calipers or micrometers are used to take accurate readings.
2. What do bearing series numbers mean?
Series numbers indicate the bearing’s dimensional and load-carrying profile. For example, common series like 6000, 6200, and 6300 all represent single-row deep groove ball bearings, but with varying widths and load capacities. The first digit typically tells you the type of bearing, while the second and third digits reflect the size and design.
A 6205 bearing, for instance, belongs to the 6200 series and has a specific ID, OD, and width associated with that size code. Understanding series numbers allows users to start confidently cross-reference between manufacturers.
3. Can I replace a bearing with one of a different width or OD?
In general, no – unless your design allows for it. Changing any one of the three key measurements (ID, OD, or width) can compromise fitment, alignment, or load distribution.
However, in some situations, adapters or sleeves can accommodate size differences. Always consult a mechanical engineer or technical sales rep before using a bearing with alternate dimensions. Even a small size change can affect radial and axial load performance or create clearance issues.
4. What is the difference between metric and inch-sized bearings?
Metric bearings use millimeters for ID, OD, and width, while inch-sized (or imperial) bearings use fractional inch or decimal measurements. Metric is more common globally and dominates industrial applications, but imperial sizes are still widely used in older equipment or North American OEMs.
One isn’t inherently better than the other; it’s more about compatibility with your existing shafts and housings. If you’re retrofitting, it’s important to match the original measurement system or confirm that adapters are available.
5. Do bearing size charts apply across all brands?
Generally, yes, especially for standard metric and imperial bearings that adhere to ISO or ABMA dimensional standards. That said, certain specialty brands may have proprietary series or geometry variations, especially in machining, defense, or precision machining sectors.
In those cases, cross reference tools or assistance from a trusted distributor is key. We specialize in helping customers navigate this gray area – especially when dealing with mixed-brand inventories or discontinued series.
How to Select the Ideal Bearings Size for Your Unique Application
Selecting the right dimensions for your equipment comes down to two paths: either you have the part number, or you don’t. If you already know the exact part number, great. That’s your direct route to finding a drop-in replacement.
But what if the number is worn off, missing, or the part is obsolete?
In that case, your best move is to measure the bearing’s inner diameter (ID), outer diameter (OD), and width, and take note of any details like seal type, cage material, clearance code or preload.
Combine that with the context of your application – what type of machine it is, how fast it spins, and the kind of load it supports – and you’ve got the data a distributor needs to help you source the correct replacement.
Don’t guess. Don’t compromise.
We specialize in helping customers navigate incomplete specs and unusual applications. Whether you’re trying to match a discontinued OEM unit or simply need a trusted second opinion, our team will work with you to identify the ideal replacement quickly. With a wide selection of precision bearings in stock (across sizes, types, and brands) and fast shipping, we make the sourcing process simple.
Need help identifying the right size? Browse our eBay store or contact us directly with your specs. We’re here to make sure you get exactly what your equipment needs.
