The 686 bearing is a miniature deep groove ball bearing widely used in applications where space is limited but rotational precision is required. With an inner diameter of 6 mm, an outer diameter of 13 mm, and a width of 3.5 mm, this bearing fits into compact mechanical assemblies across medical devices, electric bicycles, RC vehicles, and precision instruments. What are the exact specifications of a 686 bearing? What materials are used in its construction? And how do you choose between open, shielded, and sealed variants? This guide provides comprehensive answers to these questions.
Below are the complete specifications for the standard 686 bearing:
| Parameter | Value |
|---|---|
| Bearing No. | 686 |
| Bore (d) | 6 mm |
| Outer (D) | 13 mm |
| Width (B) | 3.5 mm |
| Weight | 1.87 g |
| Dynamic Load Rating (Cr) | 1.35 kN |
| Static Load Rating (C0r) | 0.44 kN |
| Fatigue Load Limit (Cu) | 0.010 kN |
| Limiting Speed (Grease) | 48,000 min⁻¹ |
| Limiting Speed (Oil) | 57,000 min⁻¹ |
| Ball Quantity | 8 |
| Ball Diameter | 2.000 mm |
The 686 bearing belongs to the 600 series of miniature ball bearings and is also known by equivalent designations such as NMB L-1360. Its counterpart with flanges is designated as LF-1360 or F686.
Technical Specifications and Performance Characteristics
Load Capacity
The 686 bearing is designed primarily to accommodate radial loads, which are forces acting perpendicular to the shaft axis. With a dynamic load rating of 1.35 kN and a static load rating of 0.44 kN, this bearing can support moderate loads relative to its compact size. Deep groove ball bearings like the 686 can also handle limited axial (thrust) loads—approximately 20% of the radial load capacity.
When selecting a 686 bearing for an application involving both radial and axial loads, engineers should calculate the equivalent load to ensure the bearing operates within its rated capacity. A safety margin of 20–30% above calculated loads is often recommended to accommodate unexpected load variations.
Speed Capability
The limiting speed of a 686 bearing depends on the lubrication method. When grease-lubricated, the maximum rotational speed is 48,000 min⁻¹. With oil lubrication, the bearing can achieve up to 57,000 min⁻¹. These high-speed capabilities make the 686 bearing suitable for applications such as dental handpieces and small electric motors where rapid rotation is required.
For applications exceeding standard speed limits, ceramic hybrid variants (silicon nitride balls with steel rings) are available. These can achieve speeds significantly higher than standard steel bearings—typically up to 60,000 rpm or more, depending on lubrication and cage design. Ceramic balls generate less frictional heat and allow higher rotational speeds without compromising bearing life.
Material and Temperature Range
Standard 686 bearings are manufactured from chrome steel (SAE 52100 or GCr15). The operating temperature range for chrome steel 686 bearings is -30°C to 110°C. For environments involving moisture, chemicals, or extreme temperatures, stainless steel (AISI 440C) or ceramic variants provide enhanced corrosion resistance and thermal stability.
Material Composition of 686 Bearings
Inner and Outer Rings
The inner and outer rings of a 686 bearing are manufactured from hardened steel with precisely ground raceways. The deep groove geometry of the raceways allows the bearing to accommodate both radial and axial loads while maintaining smooth rolling motion.
Standard rings use chrome steel SAE 52100 or GCr15, which provides excellent hardness and wear resistance. For applications requiring corrosion resistance, stainless steel AISI 440C rings are available. The inner ring has a bore diameter of 6 mm with a tolerance of -0.008 mm to 0, while the outer ring diameter of 13 mm carries the same tolerance.
Balls (Rolling Elements)
The 686 bearing contains eight precision-ground balls, each with a diameter of 2.000 mm. Standard balls are made from chrome steel. For high-speed or high-temperature applications, ceramic balls made from silicon nitride (Si₃N₄), zirconia (ZrO₂), or silicon carbide (SiC) are available. Ceramic balls offer lower density, higher hardness, and superior thermal properties compared to steel, though at a higher cost.
Cage (Retainer)
The cage maintains even spacing between the balls, preventing contact and ensuring smooth operation. For standard 686 bearings, the cage is typically a ribbon-type retainer made from stainless steel or polyamide (nylon). Stainless steel cages offer durability in high-temperature environments, while nylon cages provide lighter weight and quieter operation for lower-speed applications.
Bearing Closure Types: Open, ZZ, and 2RS
The 686 bearing is available with three primary closure configurations. Understanding the differences between these types is essential for selecting the right bearing for a given application environment.
Open Type
Open 686 bearings have no shields or seals. They offer the lowest friction and highest speed capability but provide no protection against contaminants. Open bearings are suitable for applications with clean operating environments and where external lubrication systems are available.
ZZ Type (Double Metal Shields)
686 ZZ bearings feature two non-contact metal shields, one on each side. The shields prevent larger particles from entering the bearing while allowing some lubricant flow and heat dissipation. ZZ bearings offer a balance between protection and low friction, making them suitable for general industrial environments. Metal shields are the most common closure type for 686 bearings in applications such as RC vehicles and 3D printers.
2RS Type (Double Rubber Seals)
686 2RS bearings incorporate two contact-type rubber seals. These provide superior protection against moisture, dust, and fine contaminants compared to metal shields. However, the contact seals generate higher frictional torque and reduce the maximum allowable speed. 2RS bearings are recommended for harsh environments or applications requiring extended maintenance intervals.
Selection Guide
| Environment | Recommended Type |
|---|---|
| Clean, oil-lubricated | Open |
| General industrial, low contamination | ZZ |
| Dusty, moist, or outdoor | 2RS |
| High-speed, low contamination | ZZ or Open |
Common Applications of 686 Bearings
Medical Equipment
The 686 bearing is widely used in medical devices requiring precise motion control and smooth operation. Dental handpieces, in particular, rely on miniature bearings like the 686 to achieve high rotational speeds while maintaining accuracy and patient safety. The compact dimensions of the 686 bearing also make it suitable for surgical instruments, diagnostic equipment, and laboratory devices where space is constrained.
Electric Bicycles
In electric bicycles, 686 bearings are commonly found in pedal assemblies and other rotating components. The bearing’s ability to handle moderate loads while maintaining low rotational friction contributes to efficient power transfer and smooth pedaling operation.
RC Cars and Drones
Remote-controlled vehicles and drones require lightweight, compact bearings that can operate at high speeds. The 686 bearing meets these requirements with its small form factor and high-speed capability. Hobbyist-grade motors in RC cars, planes, and drones frequently use 686 bearings, particularly the shielded ZZ variant, to protect against dust and debris encountered during outdoor operation.
Mechanical Equipment and 3D Printers
Industrial automation equipment, small robotics joints and actuators, and 3D printers all benefit from the precision and compact size of the 686 bearing. In 3D printers, these bearings are used in filament drive mechanisms and motion systems where consistent rotation and minimal play are required.
Additional Applications
Other applications for the 686 bearing include small electric motors, fans, fishing reels, skateboards, and precision instruments such as cryogenic coolers and gyroscopes.
Common 686 Bearing Variants
Standard 686 vs. 686ZZ vs. 6862RS
As discussed in the previous section, the suffix indicates the closure type. 686 denotes an open bearing, 686ZZ indicates double metal shields, and 6862RS indicates double rubber seals. All three share the same 6 mm × 13 mm × 3.5 mm dimensions and basic load ratings.
F686 (Flanged Type)
The F686 bearing incorporates a flange on the outer ring, simplifying axial positioning in housings. The flange diameter is 15 mm, with a flange width of 1.10 mm. This variant is particularly useful in applications where a snap ring or other axial retention method would be impractical.
S686 (Stainless Steel)
S686 bearings use stainless steel for both rings and balls, providing corrosion resistance for applications exposed to moisture or chemicals. The dynamic load rating for stainless steel variants is slightly lower than chrome steel, but the trade-off is acceptable for many medical and food-processing applications.
Ceramic Hybrid 686
Ceramic hybrid 686 bearings combine steel rings with ceramic balls. These bearings offer higher speed capability (often exceeding 60,000 rpm), lower operating temperatures, and electrical insulation properties. They are specified for high-precision applications such as aerospace instruments and high-speed spindles.
Selection Considerations for 686 Bearings
Load Requirements
Determine whether the application involves primarily radial loads, axial loads, or a combination. For applications with significant axial loading, verify that the calculated equivalent load does not exceed the bearing’s dynamic or static rating.
Speed Requirements
Consider the operating speed relative to the bearing’s limiting speed. For speeds approaching 48,000 rpm or higher, oil lubrication may be necessary. If the application requires speeds beyond standard limits, ceramic hybrid variants should be evaluated.
Environmental Conditions
Assess the operating environment for contaminants, moisture, and temperature extremes. For dusty environments, shielded (ZZ) or sealed (2RS) bearings are recommended. For wet or corrosive environments, sealed stainless steel (S6862RS) bearings provide the best protection.
Precision and Tolerance
Standard 686 bearings meet ABEC 1 tolerance class. For applications requiring higher precision, ABEC 3, 5, 7, and 9 grades are available from specialty manufacturers. Higher precision grades reduce runout and improve rotational accuracy but increase cost.
Maintenance and Handling Guidelines
Cleaning and Inspection
Regular inspection of 686 bearings helps identify contamination, wear, or damage before failure occurs. Use a non-corrosive solvent for cleaning, followed by thorough drying before relubrication. If excessive wear or damage is observed, replace the bearing immediately.
Lubrication Management
For miniature bearings like the 686, proper lubrication is essential for performance and longevity. Lithium-based grease is the most widely used lubricant for general applications, offering excellent quietness and durability. The standard grease fill amount for miniature bearings is approximately 25–35% of internal volume.
For high-speed applications exceeding 50,000 rpm, synthetic ester lubricants are recommended to reduce frictional heat. For extreme temperature environments ranging from -40°C to 300°C, perfluoropolyether (PFPE) grease provides stable performance.
Installation Precautions
When installing 686 bearings, ensure proper alignment to prevent uneven load distribution. Use appropriate tools for pressing the bearing into housings or onto shafts—direct hammering can cause raceway indentations and significantly reduce bearing life. For applications requiring adhesive mounting, clean the bearing surfaces with an alcohol-dampened cloth to remove anti-corrosion oil before applying adhesive.
Conclusion
The 686 bearing is a versatile miniature deep groove ball bearing with precise 6 mm × 13 mm × 3.5 mm dimensions. Its 1.35 kN dynamic load rating and 48,000 rpm grease-lubricated speed limit make it suitable for applications ranging from medical devices and electric bicycles to RC vehicles and 3D printers. Available in open, ZZ (double metal shield), and 2RS (double rubber seal) configurations, as well as flanged (F686) and stainless steel (S686) variants, the 686 bearing can be tailored to specific operating environments and performance requirements. Proper selection based on load, speed, and environmental factors, combined with regular maintenance and correct installation, ensures reliable operation and extended service life.
Frequently Asked Questions (FAQs)
Q1: What are the exact dimensions of a 686 bearing?
A1: The 686 bearing has an inner diameter (bore) of 6 mm, an outer diameter of 13 mm, and a width of 3.5 mm. The weight is approximately 1.87 grams.
Q2: What is the difference between 686, 686ZZ, and 6862RS bearings?
A2: All three share the same dimensions. 686 is an open bearing with no protection. 686ZZ has two metal shields (non-contact) for basic contamination protection. 6862RS has two rubber seals (contact) providing superior protection against moisture and dust but higher friction.
Q3: What is the load capacity of a 686 bearing?
A3: The dynamic load rating (Cr) is 1.35 kN, and the static load rating (C0r) is 0.44 kN for chrome steel variants.
Q4: What is the maximum speed of a 686 bearing?
A4: With grease lubrication, the limiting speed is 48,000 min⁻¹. With oil lubrication, the limiting speed increases to 57,000 min⁻¹. For ceramic hybrid 686 bearings, the maximum speed can exceed 60,000 rpm depending on lubrication and cage design.
Q5: What materials are 686 bearings made from?
A5: Standard 686 bearings use chrome steel (SAE 52100 or GCr15) for rings and balls. Stainless steel (AISI 440C) and ceramic hybrid (silicon nitride balls) variants are also available for specialized applications.
Q6: Where are 686 bearings commonly used?
A6: Common applications include medical and dental equipment (such as handpieces), electric bicycle pedal assemblies, RC cars and drones, 3D printers, small electric motors, and precision instruments.
Q7: How do I choose between ZZ and 2RS for my application?
A7: Choose ZZ (metal shields) for general industrial environments with low contamination levels where lower friction is prioritized. Choose 2RS (rubber seals) for harsh environments involving dust, moisture, or outdoor operation where maximum protection is required.
Q8: What lubricant should I use for a 686 bearing?
A8: Lithium-based grease is suitable for most general applications. For high-speed applications (>50,000 rpm), use synthetic ester lubricants. For extreme temperatures (-40°C to 300°C), use perfluoropolyether (PFPE) grease.
Q9: Is there a flanged version of the 686 bearing?
A9: Yes, the F686 (or LF-1360) is a flanged variant with a flange diameter of 15 mm and flange width of 1.10 mm, simplifying axial positioning in housings.
Q10: What is the operating temperature range for a standard 686 bearing?
A10: Standard chrome steel 686 bearings operate within -30°C to 110°C. Stainless steel and ceramic variants offer extended temperature ranges for specialized applications.
