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684 / 684ZZ / 684-2RS Ultra-Miniature Ball Bearing (4mm x 9mm x 2.5mm / 4mm)
- · Inner Diameter: 4mm
- · Outer Diameter: 9mm
- · Width: 4mm
- · Precision Rating: P0
- · Clearance: C0
- · Sealing Type: ZZ
- · Number of Row: Single Row
- · Material: chrome steel
- · Grease RPM Limit: 2000 RPM
- · Lubrication: Grease
Product Overview
High-Precision 684 / 684ZZ / 684-2RS Ultra-Miniature Deep Groove Ball Bearing
The 684 / 684ZZ Ultra-Miniature Ball Bearing is a metric single-row thin-section deep groove ball bearing engineered for high-precision, low-vibration, and high-speed rotary applications. Featuring an inner bore size of 4.0mm and an outer diameter of 9.0mm, the 684 series is offered in standard width configurations: 2.5mm for the unshielded Open design and 4.0mm for the dual metal-shielded 684ZZ / rubber-sealed 684-2RS variants.
High-Grade Chrome Steel & Contamination Protection
Manufactured from high-carbon chromium bearing steel (GCr15 / AISI 52100), the inner ring, outer ring, and precision micro balls undergo specialized thermal heat treatment to achieve high surface hardness (HRC 60-65) and structural fatigue strength. For clean environments requiring maximum rotational efficiency, the Open model provides minimal friction, while the 684ZZ metal-shielded version retains factory grease and shields raceways against ambient dust and foreign particulates.
Low Friction & Smooth High-Speed Performance
Equipped with precision-honed raceway grooves and a balanced ribbon cage, the 684 bearing achieves smooth, quiet running performance at speeds up to 63,000 RPM under oil lubrication. Its tight dimensional tolerances ensure reliable radial support and minimal axial play in micro-spindle assemblies.
Custom Manufacturing & Material Options
To support specialized industrial and OEM application environments, custom configurations are available upon request:
- Stainless Steel Options: Stainless steel (SUS440C / SUS304) construction for damp, corrosive, or medical-grade environments.
- Flanged Ring Design: Flanged outer ring model (F684 / F684ZZ) available for simplified housing mounting and axial location.
- Ceramic Hybrid Options: Silicon nitride (Si3N4) ceramic ball options for ultra-high-speed, low-inertia performance.
- Precision Grading: Available in ABEC-1, ABEC-3, ABEC-5, and ABEC-7 tolerance classes.
Technical Specifications
| Inner Diameter | 4mm |
| Outer Diameter | 9mm |
| Width | 4mm |
| Precision Rating | P0 |
| Clearance | C0 |
| Sealing Type | ZZ |
| Number of Row | Single Row |
| Material | chrome steel |
| Grease RPM Limit | 2000 RPM |
| Lubrication | Grease |
| Size | 4*9*4MM |
| Certificate | ISO9001 |
| Weight | 0.01(kg) |
Key Features
Applications
