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When standard carbon steel bearings corrode, seize, or fail in wet, dusty, or chemically exposed environments, engineers and hobbyists alike reach for 440 stainless steel deep groove ball bearings. Whether you are building a marine-grade mechanism, a food-processing fixture, or a high-cycle RC drivetrain, these bearings deliver the dimensional accuracy and surface durability that keeps your assembly running without unplanned downtime.
This listing covers the S684 through S699 series — twelve distinct sizes spanning bore diameters from 4 mm (0.157 in) to 9 mm (0.354 in), outer diameters from 9 mm (0.354 in) to 20 mm (0.787 in), and widths from 4 mm to 6 mm. Each bearing is manufactured from AISI 440-grade stainless steel with a ground raceway and a full complement of chrome-steel or stainless balls, depending on the variant. Available in quantities of 1, 2, 3, 5, 10, or 20 pieces per order to suit both prototyping and production runs.
Typical use cases include miniature motor shafts in RC cars and drones where splash resistance is critical, spindle assemblies in compact CNC routers where dimensional repeatability matters, and medical or laboratory equipment where corrosion from cleaning agents must be avoided. The deep groove geometry also allows these bearings to handle moderate axial loads alongside their primary radial duty — a practical advantage in multi-axis mechanisms.
🔩 AISI 440 Stainless Steel Construction
The inner ring, outer ring, and rolling elements are formed from 440-grade stainless steel, providing measurable resistance to rust, oxidation, and mild chemical exposure without requiring additional surface coatings.
📐 Twelve Size Options in One Listing
S684 (4×9×4 mm) through S699 (9×20×6 mm) — select the exact bore and OD combination your application requires. All dimensions conform to ISO 15 miniature bearing standards for drop-in interchangeability.
🔇 Low-Noise, Ground Raceway
The raceway surfaces are precision-ground to reduce vibration and audible noise at operating speeds typically up to 20,000 RPM (varies by size and lubrication), making these suitable for servo motors, spindles, and sensor assemblies where noise is a design constraint.
💧 Splash and Humidity Resistance
440 stainless steel maintains structural integrity in humid, splash-prone, or lightly corrosive environments — a direct advantage over uncoated carbon steel bearings in outdoor robotics, marine hardware, and washdown-adjacent equipment.
📦 Flexible Pack Quantities
Order 1, 2, 3, 5, 10, or 20 pieces per variant. Smaller quantities suit prototyping and repair; larger packs reduce per-unit cost for production or maintenance stock.
🔄 Deep Groove Geometry for Combined Loads
The deep groove profile accommodates both radial and moderate axial (thrust) loads in either direction, reducing the need for separate thrust washers in compact assemblies such as gearboxes, pump impellers, and actuator lead screws.
| Series | S684, S685, S686, S687, S688, S689, S694, S695, S696, S697, S698, S699 |
|---|---|
| Material | AISI 440 Stainless Steel (rings & balls) |
| Bore Diameter (ID) Range | 4 mm – 9 mm (0.157 in – 0.354 in) |
| Outer Diameter (OD) Range | 9 mm – 20 mm (0.354 in – 0.787 in) |
| Width (Thickness) Range | 4 mm – 6 mm (0.157 in – 0.236 in) |
| Bearing Type | Deep Groove Ball Bearing (Open, unshielded) |
| Dimensional Standard | ISO 15 Miniature Bearings |
| Radial Load Capacity | See variant options |
| Axial Load Capacity | Moderate (deep groove geometry); see variant options |
| Operating Speed | See variant options |
| Operating Temperature | Typically –20°C to +120°C (–4°F to +248°F) |
| Lubrication | Contact us to confirm (grease or oil per application) |
| Available Quantities | 1, 2, 3, 5, 10, 20 Pcs |
Match the bearing bore (ID) to your shaft diameter and the outer diameter (OD) to your housing bore. The width (thickness) must fit within your available axial space. Use the "ID × OD × Thickness" option selector to find the exact size. If your shaft is 6 mm, for example, you would choose S686 (6×13×5 mm) or S696 (6×15×5 mm) depending on the OD your housing accepts.
Both series share similar bore diameters (4–9 mm) but differ in outer diameter and width. The S69x series (S694–S699) generally has a larger OD for the same bore, providing higher load capacity and a wider contact footprint. Choose S68x for space-constrained designs and S69x where higher radial stiffness is needed.
These are open (unshielded) bearings. They allow for re-lubrication and are suitable for clean or lightly contaminated environments. If your application involves significant dust, debris, or liquid ingress, consider adding external seals or selecting a shielded variant. Contact us if you need shielded or sealed versions of these sizes.
AISI 440 stainless steel offers substantially better corrosion resistance than standard GCr15 (52100) carbon steel bearings. It resists rust in humid air, fresh water splash, and mild acidic or alkaline environments. However, it is not fully immune to chloride-rich environments (e.g., saltwater immersion) — for those conditions, 316 stainless or ceramic bearings are more appropriate.
Yes. The deep groove geometry allows these bearings to carry moderate axial loads in both directions alongside their primary radial load. They are not designed for pure thrust applications — for high axial loads, angular contact or thrust bearings are more suitable. For combined radial and moderate axial loads (common in motors, gearboxes, and actuators), these bearings perform well.
For most applications, a light lithium-based grease (NLGI Grade 2) applied sparingly to the raceway is sufficient. For high-speed or low-torque applications, a light spindle oil may be preferable. Re-lubrication interval depends on operating speed, load, and environment — typically every 500–2,000 operating hours for moderate-duty use. Contact us to confirm lubrication recommendations for your specific conditions.
Yes. The S684–S699 size range is widely used in RC vehicles, brushless motor assemblies, drone arm pivots, and robotic joint mechanisms. The stainless steel construction handles the vibration, occasional moisture exposure, and repeated load cycles typical of these applications. The small bore sizes (4–9 mm) align with common motor shaft diameters in this segment.
