Short answer: chrome steel bearings (AISI 52100, also called GCr15 or 100Cr6) are the standard choice: hard, strong and economical, but they rust if they get wet. Stainless steel bearings (usually AISI 440C) resist water and humidity much better, at the cost of a somewhat lower load capacity and a higher price. Choose stainless when moisture, cleaning or outdoor use is part of the job; otherwise chrome steel is the better value.
What are stainless steel bearings?
A stainless steel bearing has its rings and balls made from a stainless steel, almost always the martensitic grade 440C for precision ball bearings. 440C contains a lot of chromium (roughly 16-18%) and enough carbon to be hardened, so it combines corrosion resistance with the hardness a rolling bearing needs. Shields are normally stainless as well. Manufacturers usually mark them with an S prefix or an SS suffix; ours carry "SS", such as 623ZZ SS.
What is chrome steel (52100 / GCr15)?
Chrome steel is the high-carbon bearing steel used in most rolling bearings in the world. It is known as AISI 52100 in the US, 100Cr6 in Europe and GCr15 in China; the grades are very close. It contains around 1.5% chromium, which is far too little to make it stainless. Through-hardened, it reaches a high hardness and gives the best fatigue life of the common bearing steels, which is why it is the standard material for most rolling bearings.
Stainless steel vs chrome steel bearings: comparison
| Chrome steel 52100 / GCr15 | Stainless steel 440C | |
|---|---|---|
| Corrosion resistance | Low: rusts in water and humid air without grease | Good against water, humidity and many mild chemicals |
| Hardness | Higher | Slightly lower |
| Load capacity | Reference | Lower than chrome steel of the same size (manufacturers typically quote a reduced rating) |
| Magnetic | Yes | Yes (440C is martensitic) |
| Price | Lower | Higher |
| Typical uses | 3D printers, machines, tools, skate wheels, indoor mechanisms | Fishing reels, marine and outdoor kit, food and lab equipment, parts that are washed |
Are stainless steel bearings better?
Only in a wet or corrosive environment. In a dry machine, a chrome steel bearing is harder, carries more load and costs less, so it is the better choice. A stainless bearing pays off where a chrome bearing would rust: a rusty race quickly becomes rough and noisy, and the bearing is then finished no matter how strong the steel is.
Stainless is also not the same as rust-proof. 440C can still stain or pit in salt water, chloride cleaners or acids, particularly if it is left wet. Rinse and dry stainless bearings after salt water use, as anglers do with reels.
Precision: ABEC and ISO classes
Material and precision class are separate properties. Precision class is not stated for our bearings; if your design needs a specific ABEC or ISO class, ask us before ordering. See our guide to reading bearing codes for how ABEC and P classes compare.
Seals and shields on stainless bearings
A stainless bearing is only as water-resistant as its closure and its grease. Metal shields (ZZ) keep out larger dirt but let water in; rubber seals (2RS) keep out splashes far better. Our stainless bearings are ZZ shielded, so in very wet conditions combine them with a housing that sheds water. The ZZ vs 2RS guide explains the difference.
Stainless steel bearings vs ceramic
"Ceramic bearings" can mean two things: hybrid bearings with steel rings and ceramic balls, or full ceramic bearings. Silicon nitride (Si3N4) balls are lighter, harder, non-magnetic and electrically insulating, and they do not rust. Hybrid bearings are used for high speeds and in electric motors where current would damage steel balls. Full ceramic bearings are niche parts for chemical and extreme environments. We sell ceramic balls; we do not specify their ceramic type or grade. The ball materials are compared in our steel ball grades guide.
Are stainless steel bearings magnetic?
Yes, 440C bearings are magnetic, just like chrome steel. Austenitic stainless steels such as 304 and 316 are largely non-magnetic, but they cannot be hardened enough for precision ball bearings, so bearings made from them are a special case for low loads. If a part must be non-magnetic, look at ceramic balls instead.
Looking after chrome and stainless bearings
Most bearing failures in hobby and repair use come from dirt, water and poor fitting rather than from the steel itself. Keep chrome steel bearings in their packaging until you fit them, because the thin film of preservative oil on the rings protects them from rust in storage; do not wash it off with solvent. Press a bearing in by the ring that is being fitted (the outer ring into a housing, the inner ring onto a shaft), never through the balls, so you do not dent the raceways. If a chrome steel bearing has been wet, dry it and spin it with a little fresh lubricant on the outside, or replace it once it feels rough. For stainless bearings the same fitting rules apply; they simply forgive an occasional splash far better.
How to choose
- Dry indoor machine, 3D printer, tools: chrome steel, for example 623ZZ or 608ZZ.
- Water, humidity, outdoor, washing: stainless 440C, for example 608ZZ SS, MR105ZZ SS or 688ZZ SS.
- Dirt and splashes but not constant wet: chrome steel with 2RS seals, from our 2RS sealed bearings.
- Non-magnetic balls: ceramic balls.
All stainless bearings and stainless balls are grouped in our stainless steel bearings collection; stainless and chrome steel balls are in precision balls. Each product page lists the material, the seal and the dimensions in millimetres.