| Designation | Type | d bore | D outside | B width |
|---|---|---|---|---|
| 608 | Deep groove ball | 8 | 22 | 7 |
| 6000 | Deep groove ball | 10 | 26 | 8 |
| 6200 | Deep groove ball | 10 | 30 | 9 |
| 6201 | Deep groove ball | 12 | 32 | 10 |
| 6202 | Deep groove ball | 15 | 35 | 11 |
| 6203 | Deep groove ball | 17 | 40 | 12 |
| 6204 | Deep groove ball | 20 | 47 | 14 |
| 6205 | Deep groove ball | 25 | 52 | 15 |
| 6800 | Deep groove ball | 10 | 19 | 5 |
| 6900 | Deep groove ball | 10 | 22 | 6 |
Nominal ISO boundary dimensions for reference. Confirm against your drawing and the supplier datasheet.
Why use stainless steel bearings
Standard bearings are made of high-carbon chromium steel, GCr15, comparable to AISI 52100 and 100Cr6. It is hard and durable, but it rusts when wet. In a bottling plant, a meat line, a marine winch or a chemical mixer, a chrome steel bearing can corrode, seize or contaminate the product within weeks. Stainless steel bearings keep their rings and balls rust-free, so they stay in service under washdown, humidity, salt spray and mild chemicals. They also hold up under frequent cleaning with water, detergents and sanitising agents.
Stainless is not a free upgrade. It costs more, it carries less load than chrome steel in the same size, and the right grade matters. The desk helps buyers choose the grade, the seal and the grease in the right combination for the duty.
440C versus AISI 304
| Grade | Type | Hardness | Corrosion resistance | Typical use |
|---|---|---|---|---|
| 440C | Martensitic, hardenable by heat treatment | High enough for rolling contact | Good in water, food, mild chemicals | Rings and balls of stainless ball bearings |
| AISI 304 | Austenitic, not hardenable | Soft; cannot carry rolling loads | Better in many chemicals | Housings, shields, light-duty or low-load bearings with plastic or glass balls |
The grade that makes a real rolling bearing is 440C: it can be hardened to the level rolling contact demands. AISI 304 is more corrosion-resistant in some chemicals but cannot be hardened, so bearings that use it for rings are for light load, slow speed and wet environments, typically with glass or polymer balls, and the load ratings are well below those of 440C. Always ask which grade is used for the rings, the balls, the cage and the shields, because a stainless label on the box says little on its own. Material certificates are available per lot, confirmed in the specification.
Lower load, so size accordingly
440C stainless carries less load than chrome steel of the same dimensions, and its dynamic and static load ratings are lower. A switch from a 6205 chrome steel bearing to a 6205 stainless bearing is a switch to a lower-rated bearing. When life matters, compare the datasheet values for load rating and speed, then calculate life with the method in ISO 281 using the stated values. If the margin is thin, a larger series (a 62 instead of a 60, or a 63 instead of a 62) can restore capacity within the same bore. See deep groove ball bearings for the series guide.
Seals and food-grade grease
- Seal choice. Rubber 2RS seals keep out spray; PTFE seals suit hot or chemical washdown; open and shielded bearings suit oil-lubricated or dry duty.
- Food-grade grease. NSF H1-type grease is selected where incidental food contact is possible. The grease is chosen for temperature, water resistance and the cleaning regime.
- Cage. Stainless, nylon or PTFE cages are available. Polymer cages are used where metal debris must be avoided.
- Relubrication. Washdown flushes grease out, so the maintenance plan should schedule fresh grease after cleaning. See the lubrication guide.
Applications
Stainless steel bearings are common on food and beverage conveyors, packaging machines, mixers, pumps, medical and laboratory equipment, marine winches, boat trailers and outdoor fixtures. For electrical insulation, high speed or chemical resistance beyond what stainless can offer, consider ceramic bearings. For stainless units with a bolt-on housing, see pillow block bearings.
Specifying a stainless bearing
A short specification avoids most mistakes. Name the designation, the grade for rings and balls, the cage, the seal or shield, the grease and the clearance group. Then describe the environment: wash water temperature, cleaning chemicals, salt exposure, speed and load. With those details the desk can shortlist plants that run stainless grinding and heat treatment routinely, which is a narrower group than the plants making standard chrome steel bearings. Where an application is borderline, the supplier can propose a trial lot with the inspection plan agreed before the batch.
Also think about the mating parts. A stainless bearing on a carbon steel shaft in a wet environment can still corrode at the shaft, and galvanic effects can appear where dissimilar metals meet in salt water. Match shaft and housing materials to the environment, not only the bearing.
Inspection and ordering
Inspection for stainless lots covers dimensions against the ordered tolerance, material identification against the specification, radial clearance, smoothness of rotation, seal fit and grease type, with packaging suited to a damp environment; see packaging and anti-rust. Typical starting quantities are 100-500 pieces per standard designation; private-label marking starts around 1,000-5,000 pieces. Stock samples ship in 3-7 working days and batch production commonly takes 25-45 days, as typical reference ranges confirmed in writing. Send designations through the quote form, and see specialty bearings for other options.