How to Read a Bearing Code

Overview Every bearing has a code stamped on its side. That combination of numbers and letters is not random. It follows the ISO 15 standard. If you have ever wondered how do you read a bearing code, the answer lies in five fixed positions that determine type, size, sealing, and internal fit. This guide walks through each one with real bearing examples.

What a Bearing Code Tells You

A standard bearing code like 6204-2RS packs four pieces of information into a short string: the bearing type, the dimensional series, the bore diameter, and the suffix for sealing and clearance. Each position has a fixed meaning under ISO 15. The system is consistent across manufacturers, which means a 6204 deep groove ball bearing from one supplier has the same boundary dimensions as a 6204 from another.

The basic designation has three sections. The first digit identifies the bearing type. The second digit or pair of digits defines the dimension series: the width and outer diameter relative to the bore. The last two digits encode the bore size. Suffixes add sealing type, cage material, internal clearance, and precision grade. Learning to parse these parts takes under 10 minutes and pays off every time you order a replacement bearing.

Bearing Type Codes

The first digit tells you what kind of bearing it is. The most common type code is 6, which identifies a single-row deep groove ball bearing. This design handles radial loads and moderate axial loads at speeds ranging from 10,000 rpm for larger sizes to over 50,000 rpm for miniature bearings.

Yuanhe manufactures type 6 deep groove ball bearings in a wide range of standard and custom bore sizes. For the single-row deep groove ball bearing, the type digit 6 is sometimes omitted in short designations. A code like 6204 is understood as type 6, dimension series 2, bore code 04.

Dimension Series

After the type digit comes the dimension series. For 6-series bearings, this is a number like 0, 2, or 3 that encodes the bearing width and outer diameter relative to the bore. Each series targets a different load and space envelope.

A 6204 bearing (series 2) has a wider cross-section than a 6004 (series 0) of the same bore. The series 2 bearing supports higher radial loads but needs more radial space in the housing. When replacing a bearing, matching the dimension series matters as much as matching the bore size. A 6004 will not fit the same housing as a 6204 even though both have a 20mm bore.

Bore Size Codes

The bore diameter is encoded in the last one or two digits. For bore sizes from 20mm to 480mm, multiply the last two digits by 5 to get the bore in millimeters. A 6204 bearing has bore code 04, so the bore is 4 x 5 = 20mm. A 6212 has code 12, giving a 60mm bore.

For bores under 10mm, the code is simply the bore diameter in millimeters: a 608 bearing has an 8mm bore, and a 626 bearing has a 6mm bore. Bores over 500mm and bores not evenly divisible by 5 use a slash separator format like 62/500 for a 500mm bore. This format appears in large industrial bearings and is uncommon in standard catalog sizes.

Suffix Codes

The suffix is where most confusion happens. A single bearing can carry multiple suffix codes stacked together, like 6204-2RS-C3. Each suffix has a specific meaning under ISO standards. The standard order for stacking is sealing first, then cage material, then internal clearance, then precision grade.

Seals and Shields

A 6204-2RS bearing is sealed on both sides with rubber lips. It comes pre-greased and does not need relubrication during its service life. A 6204-ZZ bearing has metal shields that do not touch the inner ring, allowing notably higher speeds but offering less protection against fine dust and moisture. Open bearings with no suffix for sealing are used inside oil-bath or grease-packed housings where the enclosure already provides protection.

Internal Clearance

C3 clearance is the default choice for electric motors. The extra internal space allows the inner ring to expand from operating heat without preloading the rolling elements. Yuanhe stocks deep groove ball bearings in C3 and CN clearance as standard for OEM orders.

Additional suffix codes cover cage material and precision. TN or TV9 indicates a glass-fiber reinforced polyamide cage rated to 120 C. M means a machined brass cage for higher-temperature applications. P5 and P6 correspond to ABEC-5 and ABEC-7 precision grades for applications demanding tighter bore and runout tolerances.

Reading Real Bearing Codes

Let us decode three common bearing codes found on equipment and in supplier catalogs.

When the Code Does Not Match the Standard

Not all bearing codes follow ISO 15. Some manufacturers use proprietary numbering systems. Inch-series bearings use a different system with codes like R8 or EE4. Miniature bearings under 10mm bore often use a direct three-digit code: 693 means type 6, series 9, 3mm bore, and 684 bearing means type 6, series 8, 4mm bore.

For OEM replacement applications, send the existing bearing code and the measured boundary dimensions to your supplier. Yuanhe accepts bearing drawings and cross-reference requests against 12,000+ completed OEM projects. The team matches interchange data to find the correct bearing even when the original code is proprietary or worn.

Some codes are stamped incompletely on small bearings due to space limits on the shield face. A 608 ZZ bearing may only show “608Z” on the shield. When in doubt, measure the bore, outer diameter, and width with a digital caliper and check against an interchange table. The measured dimensions resolve the ambiguity every time without needing to guess at worn or partial markings.

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