How to Read Bearing Codes: Complete ISO Decoding Guide With Lookup Tables

A bearing designation is a standardized alphanumeric code per ISO 15 that encodes the bearing type, dimensions, seals, internal clearance, and cage material into a single string — allowing an engineer to identify the exact bearing specification from the characters stamped on its outer ring.

For example, reading 6205-2RSH C3 immediately tells you: deep groove ball bearing, 25 mm bore, rubber contact seals on both sides, C3 internal clearance (greater than normal). No catalog lookup required. No phone call to the supplier. All the information sits in 13 characters.

The ability to decode bearing designations accurately prevents ordering errors — getting the bore code wrong by one digit means a 5 mm bore diameter mismatch, making the bearing impossible to mount on the shaft. Getting the clearance suffix wrong (ordering CN instead of C3 for a motor with an interference fit) leads to thermal overload and bearing failure within a few hundred operating hours.

This article breaks down every component of a bearing designation — from the type prefix to the final suffix — with full lookup tables and cross-brand comparisons for ZVL, SKF, FAG, NSK, NTN, and Timken. Reference data sourced from the designation systems of SKF, FAG/Schaeffler, NTN, and ISO 15:2017.

Basic Designation Structure

Every ISO bearing designation consists of four main segments, read left to right:

[Type Prefix] + [Dimension Series] + [Bore Code] + [Suffixes]

The prefix identifies the rolling element type (ball, cylindrical roller, tapered roller, spherical roller). The dimension series — two digits — encodes the width and outside diameter. The bore code — the last two digits of the numeric portion — allows you to calculate the bore diameter. Suffixes — everything after the bore code — encode seals, clearance, cage material, and special features.

Take the designation NU 2210 ECP/C3 as a worked example:

The reading order is always fixed across all manufacturers. Some brands add proprietary characters — SKF uses ECP for polymer cages, FAG uses TVP — but the core designation (prefix, series, bore code) follows ISO 15 and reads identically across all tier-1 brands including ZVL, SKF, FAG, NSK, NTN, and Timken.

When encountering an unfamiliar bearing designation, always decode in order: prefix → series → bore code → suffixes. Never guess. Never extrapolate from an old code to a new one. Each designation must be decoded independently.

Type Prefixes

The prefix is the first element to identify. No letter prefix means a deep groove ball bearing (DGBB) — the most common bearing type worldwide, accounting for over 40% of global bearing production according to the SKF Annual Report 2023.

Complete Prefix Table

Quick identification rules: code starts with 6 or has no letter prefix — ball bearing. Starts with NU, NJ, NUP, or N — cylindrical roller. Starts with 3 followed by four digits (30xxx or 32xxx) — tapered roller. Starts with 22 or 23 — spherical roller. Starts with 7 — angular contact. Starts with 5 — thrust.

Timken uses a proprietary system for many tapered roller bearings. Example: Timken 30210 = ISO 32210. When cross-referencing between brands, always verify against official catalogs or equivalence tables.

Dimension Series

The dimension series consists of two digits: the first digit is the width series, and the second digit is the outside diameter series.

In the designation 6205: the digit 2 is the outside diameter series (medium). In NU 2210: the digits 22 mean width series 2 + diameter series 2.

Outside Diameter Series: 62xx vs 63xx vs 64xx

The diameter series determines the outside diameter (D) for a given bore diameter (d). Higher numbers mean larger OD and higher load capacity.

For the same 25 mm bore, a series 3 bearing (6305) has a dynamic load rating C = 22.5 kN — 1.5 times that of series 2 (6205, C = 14.8 kN). Series 4 (6405) reaches 36.3 kN but requires an 80 mm housing bore, demanding a significantly larger bearing seat.

Width Series

The width series determines the bearing width (B). For deep groove ball bearings (6000 series), nearly all use width series 0 (standard) — this digit is typically omitted from the designation. Cylindrical roller bearings and spherical roller bearings frequently use width series 1, 2, or 3 to increase the number of rollers and load capacity.

Specific example: NU 210 (width 0) has B = 20 mm, NU 2210 (width 2) has B = 23 mm, NU 310 (width 0 but diameter series 3) has B = 27 mm. Higher width series = wider bearing = more rollers = higher load capacity.

Practical Selection Rules

The majority of electric motor, pump, and industrial fan applications use series 2 (62xx) or series 3 (63xx). Series 2 is more common because it balances load capacity against housing size. Upgrade to series 3 when the applied load exceeds 60–70% of the series 2 dynamic load rating C, or when a longer L₁₀ life is required under the same load.

Bore Code Rules

The bore diameter (symbol d) is the single most important parameter when ordering a bearing. The bore code encoding has three distinct zones — and four mandatory exceptions.

The ×5 Rule for d ≥ 20 mm

From d = 20 mm upward: bore code = d ÷ 5.

• d = 20 mm → bore code 04
• d = 25 mm → bore code 05
• d = 50 mm → bore code 10
• d = 100 mm → bore code 20
• d = 200 mm → bore code 40

This rule applies to approximately 95% of bearings used in industrial practice.

Four Exceptions for d < 20 mm

These four codes must be memorized. There is no formula that derives d = 10 mm from bore code 00, or d = 17 mm from bore code 03.

Small Bearings (d < 10 mm) and Large Bearings (d ≥ 500 mm)

• d < 10 mm: Written directly. Example: 625 has bore code 5, meaning d = 5 mm. Some designations use a slash: 630/4 means d = 4 mm.
• d ≥ 500 mm: Written directly in mm, separated by a slash. Example: 618/500 means d = 500 mm.

Bore Code Lookup Table (00 to 96)

Beyond bore code, the geometric tolerance class (P0, P6, P5, P4, P2) also affects bore diameter tolerances. When ordering bearings from a supplier, always verify the bore diameter by physical measurement or by checking the manufacturer's official catalog. A single-digit bore code error translates to a 5 mm bore mismatch — enough to make the bearing impossible to mount on the shaft.

Suffix Group 1: Seals and Shields

The seal/shield suffix indicates how the bearing is protected from contamination. This suffix directly affects service life in real operating environments — dust, water, chemicals.

Cross-Brand Seal/Shield Suffix Comparison

Contact seals (2RS, 2RSH, DDU): The rubber seal lip contacts the inner ring, creating a full seal. Suitable for dusty, wet, or chemically aggressive environments. Trade-off: higher friction than shields, more heat generation, limiting speed reduced 20–30%. Used on pumps, conveyors, outdoor equipment. In food processing plants or paper mills — where bearings are regularly exposed to water — contact seals are the default choice.

Non-contact seals (2RZ): The seal lip approaches but does not touch the inner ring. Lower friction than 2RS, higher speed capability, but reduced sealing effectiveness. SKF uses 2RZ for certain medium-speed applications where the balance between protection and performance matters.

Metal shields (2Z, ZZ): Thin steel plates block dust but do not seal against water. Higher limiting speed than rubber seals. Suitable for indoor electric motors, enclosed gearboxes, and high-speed applications in clean environments.

Open bearings (no suffix): No seals or shields. Used with external lubrication systems (oil bath, oil mist) or when frequent re-greasing is required. Highest limiting speed.

Note on cross-brand differences: SKF transitioned from the older 2RS designation to 2RSH (an improved low-friction seal design) for most deep groove ball bearings. FAG uses 2RS1 or 2RSR — 2RS1 being the newer version. ZVL follows the standard ISO designation 2RS. NSK uses DDU and NTN uses LLU. Despite different suffixes, the contact seal function across all tier-1 brands is equivalent.

Suffix Group 2: Internal Clearance

Internal clearance is the total distance between the rolling elements and the raceways before mounting. When the bearing is press-fitted onto a shaft, clearance decreases. When operating at elevated temperatures, the inner ring expands — clearance decreases further. Incorrect clearance selection is one of the most common causes of premature bearing failure.

Clearance Classes per ISO 5753-1

CN (Normal) is the default. If the designation shows no clearance suffix, it means CN. The symbol CN is never printed on the bearing.

C3 is the most common clearance class in industrial applications. The reason: most electric motors use an interference fit on the shaft (h6/k5 or j5), which consumes 5–10 μm of clearance. Add thermal expansion at operating temperatures of 60–80°C, consuming another 3–5 μm. C3 ensures the bearing retains 3–10 μm of residual clearance during operation — enough for the grease film to function. According to the SKF Maintenance Handbook, over 70% of bearings installed in standard IEC electric motors use C3 clearance.

C2 is used for precision applications with very light loads, loose shaft fits, and low operating temperatures. In actual plant environments, C2 is far less common than C3 or CN.

C4 and C5 are used in kilns, dryers, applications above 100°C, or extremely tight fits. Spherical roller bearings in cement crushers typically use C4 because operating temperatures and adapter sleeve mounting consume significant clearance.

Rule of thumb: standard IEC electric motors always use C3. When in doubt, specify C3. Selecting a clearance class that is too small is more dangerous than one that is too large — insufficient clearance causes overloading, overheating, and failure within hours.

Suffix Group 3: Cage/Retainer

The cage (also called retainer) holds the rolling elements evenly spaced, guides their motion, and distributes lubricant. Cage material directly affects limiting speed, noise level, and temperature capability.

Cross-Brand Cage Suffix Comparison

Pressed steel (J): The default for most standard bearings. Durable, low cost, continuous temperature rating of 120°C. When no cage suffix is specified, most manufacturers use pressed steel for 62xx and 63xx series.

Brass (M): Used for large bearings (d > 100 mm), shock loads, or very high speeds. Continuous temperature rating of 250°C — suitable for kilns and dryers. Common in spherical roller bearings: 22220 EK with brass cage = 22220 EMK. Costs 2–3 times more than steel cages.

Polyamide PA66 (TN, TVP): 85% lighter than steel, lower noise, reduced friction. SKF uses TN9 (glass-fiber-reinforced polyamide) for high-speed ball bearings. FAG uses TVP2. Temperature limit is 120°C continuous — never use for applications above 120°C because the polymer deforms and destroys the cage.

When ordering, if your application requires a specific cage material (for example, brass for kiln applications), you must specify it explicitly in the order code. Do not assume the manufacturer will supply the correct material without explicit specification.

Suffix Group 4: Special Features

Beyond seals, clearance, and cage, numerous additional suffixes encode special features — load enhancement, tapered bore, lubrication grooves, and contact angles.

Load-Enhanced Suffixes

Tapered Bore Suffixes (K, EK)

Spherical roller bearings with the K suffix (e.g., 22220 EK) mount via adapter sleeve H320 onto a straight shaft. Advantages: easy mounting and dismounting, no press-fitting required. Common in conveyor, crusher, and vibrating screen applications — where quick maintenance turnaround is critical.

Lubrication Groove and Snap Ring Suffixes

Angular Contact Suffixes

When reading angular contact bearing designations, the suffix order is: contact angle → load enhancement → cage type → clearance. Example: 7210 BEP = 40° angle (B) + enhanced (E) + polymer (P).

Cross-Brand Designation Comparison: SKF vs FAG vs NSK vs ZVL

The core designation (prefix + series + bore code) is identical across all ISO-compliant manufacturers. Differences lie entirely in the suffixes. The table below compares the same bearing across different brands — this is the most critical cross-reference table when substituting bearings across manufacturers.

Cross-Reference Table

Key observations from the cross-reference table:

• Seals: ZVL, SKF, and FAG use different suffixes for functionally equivalent seals. ZVL 2RS = SKF 2RSH = FAG 2RS1 = NSK DDU = NTN LLU. When substituting across brands, use the table above.
• Cages: SKF uses ECP (polymer), FAG uses TVP2 (polyamide), NTN typically omits the suffix when it is the default. ZVL follows standard ISO designations.
• Spherical rollers: FAG adds E1-XL (new-generation enhanced), NSK uses EAE4. Despite different suffixes, the basic dimensions (d, D, B) comply with ISO 15 — full interchangeability is guaranteed.
• Tapered rollers: The core code 30207 is identical across most brands. SKF adds J2/Q (pressed steel cage + SKF Explorer quality). FAG adds -A (improved design).
• Thrust ball bearings (51105): The designation is identical across all brands because this type has few suffix variants.

When replacing a bearing from one brand with another, three dimensions must match exactly: bore diameter (d), outside diameter (D), and width (B). Select equivalent seal and clearance suffixes using the cross-reference table. Never change the clearance class when switching brands — if the original was C3, the replacement must also be C3.

Timken Tapered Roller Bearing Designations

Timken uses a proprietary inch-based designation system for many tapered roller bearings, completely different from ISO numbering:

For Timken inch-series designations, consult the Timken catalog directly for dimensions. The bore code × 5 rule does not apply.

Worked Examples: Decoding 5 Real Bearing Designations

Below are 5 real bearing designations, decoded segment by segment in standard order. Each example includes confirmed specifications from manufacturer catalogs.

Example 1: 6205-2RSH C3

Confirmed specifications: d = 25 mm, D = 52 mm, B = 15 mm, C = 14.8 kN, C₀ = 7.8 kN. This is the most common bearing designation in industrial use, found in electric motors from 0.75 to 7.5 kW, small centrifugal pumps, and industrial fans. Equivalents: ZVL 6205 2RS C3, FAG 6205-2RS1/C3, NSK 6205DDU C3.

Example 2: NU 2210 ECP

Confirmed specifications: d = 50 mm, D = 90 mm, B = 23 mm, C = 88 kN. Cylindrical roller bearing for high radial loads with no axial load capability. Width series 2 gives 23 mm width instead of 20 mm (NU 210), increasing the number of rollers and load capacity. ECP is an SKF designation — equivalent to FAG NU 2210-E-TVP2 or ZVL NU 2210.

Example 3: 22220 EK/C3

Confirmed specifications: d = 100 mm, D = 180 mm, B = 46 mm, C = 550 kN. The tapered bore (K) is used with adapter sleeve H320 to mount on a straight 100 mm shaft. Common in heavy conveyors, crushers, and large industrial fans. C3 clearance is mandatory because adapter sleeve mounting consumes significant clearance. Equivalents: ZVL 22220 EK C3, FAG 22220-E1-XL-K/C3.

Example 4: 30207

Confirmed specifications: d = 35 mm, D = 72 mm, B = 18.25 mm, C = 64.4 kN, C₀ = 69.5 kN. Tapered roller bearing for combined radial and axial loads, widely used in gearboxes, truck axles, and pump shafts. The code 30207 belongs to the 302 series — diameter series 0 (standard) + the leading digit 3 identifies this as a tapered roller type (not a conventional width series). When reading tapered roller codes: the first digit 3 identifies the bearing type, the next two digits (02) are the dimension series, and the last two digits (07) are the bore code. Equivalents: ZVL 30207, SKF 30207 J2/Q, FAG 30207-A, NSK 30207.

Tapered roller bearings always consist of two separable parts: the cone (inner ring + rollers + cage) and the cup (outer ring). When ordering, always confirm whether you need the complete assembly or just the cone or cup individually.

Example 5: 7210 BEP

Confirmed specifications: d = 50 mm, D = 90 mm, B = 20 mm. The 40° contact angle provides higher axial load capacity than 15° but lower limiting speed. Angular contact bearings are typically mounted in pairs — back-to-back (DB) for bidirectional axial load, or face-to-face (DF) when the shaft experiences thermal expansion. Common on machine tool spindles, vertical pump shafts, and milling machine main spindles. Equivalents: FAG 7210-B-TVP, NSK 7210B, ZVL 7210 B.

Example Summary Table

At a cement plant in Hai Duong province, an engineer received a batch of 6308-2RSH C3 bearings and needed to verify the specifications before installing them on a 22 kW exhaust fan motor. Decoding: 6 = deep groove ball bearing, 3 = heavy diameter series, 08 = bore 40 mm, 2RSH = rubber contact seals both sides, C3 = greater than Normal clearance. The specifications matched the motor's requirements — k5 shaft fit requires C3 to compensate for clearance reduction from the press fit.

At a machine shop in Dong Nai province, a maintenance technician received designation 22220 EK/C3 for a conveyor pulley shaft. Decoding: 222 = spherical roller bearing series 222, 20 = bore 100 mm, E = enhanced load design, K = tapered bore 1:12 for adapter sleeve H320, C3 = greater than Normal clearance. Confirmed correct — adapter sleeve H320 was already in stock, and installation proceeded.

At a steel plant in Ba Ria – Vung Tau province, the procurement department received a request to replace bearing 30207 for a conveyor gearbox. The maintenance engineer decoded: 3 = tapered roller, 02 = dimension series, 07 = bore 35 mm. Confirmed shaft diameter 35 mm, housing bore 72 mm. Ordered ZVL 30207 as the replacement — mounting dimensions comply with ISO 15, direct interchangeability confirmed.