Metric Sizes Open

Miniature and Small Metric-Size Bearings – Open are precision rolling bearings manufactured to metric dimensions, with bore diameters typically ranging from 1 mm to 10 mm and outer diameters from 3 mm to 30 mm. These open-configuration bearings (without seals or shields) are designed for ultra-compact mechanisms requiring minimal friction, maximum speed, and precise rotational control in metric-standard equipment.

Key Technical Features:

• Metric size standards: Conforming to ISO 15 and DIN 625 dimensions. Common series include 68, 69, 60, 62, 63, and MR (ultra-miniature) series. Typical sizes: 681 (1×3×1 mm), 694 (4×11×4 mm), 608 (8×22×7 mm), and 6200 series (10×30×9 mm).

• Open design: No seals or shields allows unrestricted lubricant flow, lowest possible torque, and highest speed capability. Open bearings accept external lubrication systems (oil mist, drip, or circulating oil) and are preferred for high-speed spindles and precision instrument applications.

• Precision grades: Available in P0 (ABEC 1) for general use, P6 (ABEC 3) , P5 (ABEC 5) , P4 (ABEC 7) , and P2 (ABEC 9) for critical high-precision applications. Miniature metric bearings routinely achieve P5 and higher tolerances.

• Materials: Chrome steel (52100) for standard applications; stainless steel (440C) for corrosion resistance; beryllium copper or M50 for specialized environments. Hybrid ceramic (Si₃N₄ balls) available for ultra-high speed and electrical insulation.

• Internal design: Deep groove geometry provides balanced radial and axial load capacity. Optimized ball complement (Grade 3, 5, or 10) and raceway surface finish (Ra ≤ 0.02 μm) minimize friction and vibration.

• Cage options: Crown-type (ribbon) cages in steel or phenolic resin; polyamide cages for low noise; full-complement designs (no cage) for maximum load capacity at reduced speeds.

• Lubrication: For open bearings, low-viscosity oils or dry lubricants (MoS₂, graphite) minimize drag torque at high speeds. Grease is not retained without seals.

• Torque characteristics: Open miniature bearings exhibit the lowest possible starting and running torque (as low as 0.1 g·cm), essential for sensitive instruments and gyroscopes.

• Speed capability: With proper lubrication, open miniature bearings can achieve speeds exceeding 100,000 RPM for the smallest sizes (1–3 mm bore), limited primarily by cage design and lubrication method.

Applications:
Open miniature metric bearings are ideal for instrumentation, gyroscopes, potentiometers, encoder sensors, flow meters, dental handpieces (400,000+ RPM), micro-turbines, miniature pumps, aerospace actuators, optical positioning stages, semiconductor manufacturing equipment, and medical devices. These precision components deliver reliable, low-friction rotation in the most demanding micro-mechanical systems.