Ball bearings nomenclature SKF FAG
Ball bearings are identified by a standardized designation system that encodes the main dimensions, type, design features, and precision specifications in a sequence of numbers and letters. The basic SKF system, widely adopted by manufacturers such as FAG and NSK, follows international standards ISO 15 and ISO 15241 to ensure dimensional and functional interchangeability.
Basic designation system
Section titled “Basic designation system”The basic designation of a ball bearing contains dimensional and typological information organized in positional blocks. A 4-digit code defines the width series, the outside diameter series, and the bore diameter of the bearing. Standard radial ball bearings usually present a type digit at the beginning that identifies the constructional family.
| Type code | Designation | Common examples |
|---|---|---|
| 6 | Single row deep groove ball bearing | 6204, 6305, 6007 |
| 16 | Thin section deep groove ball bearing | 16002, 16008 |
| 7 | Single row angular contact ball bearing | 7206, 7308 |
| 32/33 | Double row angular contact ball bearing | 3205, 3309 |
| QJ | Four-point angular contact ball bearing | QJ210, QJ312 |
| 12/22 | Self-aligning ball bearing | 1205, 2208 |
| 51/52/53 | Thrust ball bearing | 51104, 52208 |
Bore diameter designation
Section titled “Bore diameter designation”The last two digits of the basic designation represent the bore diameter of the bearing. For diameters between 20 mm and 480 mm, this value is obtained by multiplying the two digits by 5. For diameters below 20 mm or above 500 mm, special coding rules are used.
| Final digits | Bore diameter (mm / in) | Application range |
|---|---|---|
| 00 | 10 mm / 0.394 in | Bearings with d < 20 mm |
| 01 | 12 mm / 0.472 in | Bearings with d < 20 mm |
| 02 | 15 mm / 0.591 in | Bearings with d < 20 mm |
| 03 | 17 mm / 0.669 in | Bearings with d < 20 mm |
| 04 to 96 | Multiply digits × 5 mm | Bearings with 20 mm ≤ d ≤ 480 mm |
| /500 and above | Actual diameter in mm after slash | Bearings with d ≥ 500 mm |
Dimension series
Section titled “Dimension series”The third digit defines the outside diameter series and the second digit (or the type digit in combination) defines the width series. The combination of both determines the load capacity and cross-sectional dimensions of the bearing.
| Outside diameter series (3rd digit) | Width series | Dimensional description | Designation example |
|---|---|---|---|
| 0 (extra light series) | 0/1 | Very thin section bearing | 6000, 16001 |
| 2 (light series) | 2/3 | Standard light section bearing | 6205, 6305 |
| 3 (medium series) | 2/3 | Medium section bearing, higher capacity | 6308, 6310 |
| 4 (heavy series) | 2/3 | Robust section bearing, high load | 6405, 6412 |
Prefixes
Section titled “Prefixes”Prefixes are placed before the basic designation to indicate the bearing material, rolling element type, or special constructional features. The most commonly used prefixes in the SKF system are listed below.
| Prefix | Meaning | Typical application |
|---|---|---|
| W | Stainless steel bearing | Corrosive environments, food industry |
| R | Bearing with spherical outer ring | Split housings, tilting mounts |
| L | Bearing with light alloy machined cage | High rotational speed |
| BS | Thrust ball bearing, single direction load | Pure axial thrust applications |
| EE | Inch ball bearing, extra light series | Equipment manufactured under ANSI/ABMA standard |
| G | Angular contact ball bearing for universal pairing | Bearing pairs in duplex arrangement |
Common suffixes: seals
Section titled “Common suffixes: seals”The suffixes that define the seal type are applied after the basic bearing designation and indicate the degree of protection against contaminants and lubricant retention. The most frequent seals in the SKF range are listed in the following table with their maximum operating temperatures.
| Suffix | Seal type | Material | Maximum operating temperature | Main characteristic |
|---|---|---|---|---|
| 2Z | Metal shield on both sides | Steel / sheet steel | 120 °C / 248 °F | Protection against large particles, low friction |
| 2RSH | Reinforced synthetic rubber seal on both sides | Nitrile rubber (NBR) | 100 °C / 212 °F | High sealing, grease retention |
| 2RS1 | Synthetic rubber seal on both sides (single lip) | Nitrile rubber (NBR) | 100 °C / 212 °F | Standard protection, low frictional resistance |
| 2RS2 | Fluorinated rubber seal on both sides | Fluorinated rubber (FKM) | 200 °C / 392 °F | High thermal and chemical resistance |
| Z | Metal shield on one side | Steel / sheet steel | 120 °C / 248 °F | One-sided protection, access for regreasing |
| RSH | Reinforced synthetic rubber seal on one side | Nitrile rubber (NBR) | 100 °C / 212 °F | Optimized sealing |
Common suffixes: cages and materials
Section titled “Common suffixes: cages and materials”Cages guide and separate the rolling elements, and their material and design determine the speed and temperature limits of the bearing. Cage suffixes in SKF nomenclature identify the construction type and base material.
| Suffix | Cage type | Material | Maximum operating temperature | Relative speed limit |
|---|---|---|---|---|
| J | Stamped steel cage, ball centered | Steel sheet | 120 °C / 248 °F | High |
| Y | Stamped brass cage, ball centered | Brass / sheet brass | 150 °C / 302 °F | Very high |
| M | Machined brass cage, ball or race centered | Machined brass | 200 °C / 392 °F | Medium to high |
| TN9 | Glass fiber reinforced polyamide cage, ball centered | Polyamide 66 + 25% glass fiber | 120 °C / 248 °F | Very high |
| TNH | Glass fiber reinforced polyamide cage, high temperature | Modified polyamide | 150 °C / 302 °F | High |
| PHAS | PEEK cage with carbon fiber and PTFE filler | PEEK / composite | 250 °C / 482 °F | Medium |
Common suffixes: internal clearance and precision
Section titled “Common suffixes: internal clearance and precision”Internal radial clearance and dimensional precision class are critical parameters in bearing selection, especially under interference fit conditions with shafts and housings or in high-accuracy machine tools.
Internal radial clearance classes
Section titled “Internal radial clearance classes”| SKF suffix | Internal radial clearance (µm) — typical range for d=20–50 mm | Meaning | Recommended application |
|---|---|---|---|
| C1 | 0 – 8 µm / 0 – 315 µin | Radial clearance smaller than Normal | Light adjustments, low temperature |
| C2 | 3 – 15 µm / 118 – 591 µin | Reduced radial clearance | Small electric motors, light spindles |
| CN (Normal) | 5 – 20 µm / 197 – 787 µin | Standard radial clearance | General operating conditions |
| C3 | 10 – 28 µm / 394 – 1102 µin | Radial clearance larger than Normal | Interference fits, high thermal gradients |
| C4 | 20 – 40 µm / 787 – 1575 µin | Wide radial clearance | Heavy interference, high service temperature |
| C5 | 30 – 55 µm / 1181 – 2165 µin | Very wide radial clearance | Extreme thermal load and fit conditions |
Dimensional precision classes
Section titled “Dimensional precision classes”| Suffix | Equivalent ISO standard | Maximum radial deviation (d ≤ 30 mm) | Application |
|---|---|---|---|
| P0 (no suffix) | Normal class ISO 492 | 10 µm / 394 µin | Standard industrial applications |
| P6 | Class 6 ISO 492 | 7 µm / 276 µin | Intermediate precision, industrial fans |
| P5 | Class 5 ISO 492 | 4 µm / 157 µin | Machine tools, grinding spindles |
| P4 | Class 4 ISO 492 | 2.5 µm / 98 µin | High-speed spindles, measuring instruments |
| PA9A | Super precision ABEC 9 (ANSI) | 1.5 µm / 59 µin | Ultra precision instruments |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What does the code 6205-2RSH/C3 mean in SKF nomenclature?
Section titled “What does the code 6205-2RSH/C3 mean in SKF nomenclature?”The code 6205-2RSH/C3 designates a deep groove ball bearing with 25 mm / 0.984 in bore diameter, with nitrile rubber seal on both sides and internal radial clearance C3 (10–28 µm / 394–1102 µin). The basic designation 6205 breaks down into type 6 (deep groove), outside diameter series 2 (light series) and bore diameter 25 mm (05 × 5). The suffix 2RSH indicates reinforced synthetic rubber seals on both sides, with a maximum operating temperature of 100 °C / 212 °F.
What is the difference between 2RSH and 2Z seals in an SKF bearing?
Section titled “What is the difference between 2RSH and 2Z seals in an SKF bearing?”2RSH seals provide contact sealing with moderate friction and protect against fine dust and moisture, with a maximum temperature of 100 °C / 212 °F. 2Z metal shields generate no significant additional friction and withstand up to 120 °C / 248 °F, but only protect against large particles. The speed limit with 2RSH is approximately 30% lower than with 2Z due to frictional heating of the sealing lip.
How is a stainless steel bearing identified in SKF nomenclature?
Section titled “How is a stainless steel bearing identified in SKF nomenclature?”Stainless steel bearings carry the prefix W placed before the basic designation, such as W 6004-2Z. The races and rolling elements are made of AISI 440C martensitic stainless steel with a surface hardness of 58 to 62 HRC, suitable for operating temperatures up to 150 °C / 302 °F. The dynamic load capacity of these bearings is approximately 20% lower than that of equivalent standard chrome steel bearings.
What does the suffix TN9 indicate in a ball bearing?
Section titled “What does the suffix TN9 indicate in a ball bearing?”The suffix TN9 identifies a cage made of polyamide 66 reinforced with 25% glass fiber, injection molded and centered on the rolling elements. This design reduces the cage weight by approximately 60% compared to stamped steel cages, allowing speed limits up to 20% higher and quieter operation. The maximum service temperature is 120 °C / 248 °F.
What is the purpose of internal radial clearance C3 in a bearing?
Section titled “What is the purpose of internal radial clearance C3 in a bearing?”Radial clearance C3 (10–28 µm for shaft diameters of 20 to 50 mm / 0.787 to 1.969 in) compensates for the reduction in clearance caused by interference fits between the inner ring and the shaft, or between the outer ring and the housing. It also absorbs thermal expansion gradients when the bearing temperature exceeds the temperature of adjacent parts by 30 °C / 86 °F, preventing seizure and premature failure due to excessive preload.
How is an angular contact ball bearing with 30 mm bore diameter and a brass cage designated?
Section titled “How is an angular contact ball bearing with 30 mm bore diameter and a brass cage designated?”The designation 7206 BM corresponds to an angular contact ball bearing with 30 mm / 1.181 in bore diameter, a contact angle of 40° and a machined brass cage centered on the rolling elements. The number 7 identifies the type (single row angular contact), 2 indicates a light outside diameter series, and 06 codes the 30 mm bore diameter. The suffix M denotes a machined brass cage, suitable for a maximum temperature of 200 °C / 392 °F and high speed capability.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/valves-abbreviations-d_905.html
- mcmaster.com: https://www.mcmaster.com/products/bearings/bearing-type~ball-1/