The NA series comprises single-row and double-row needle roller bearings with inner rings and machined rings. Their key features include an ultra-thin radial cross-section, high rigidity, and exceptionally high pure radial load capacity. Specially designed for applications with extremely limited space, heavy loads, and medium-to-high speed rotational or oscillating conditions, they serve as core compact transmission components in automobiles, machine tools, reducers, hydraulic equipment, and other fields.

1. Core Structure and Key Advantages of NA Series Bearings

NA series bearings consist of an inner ring, outer ring, needle rollers, cage, and optional seals. The outer ring is equipped with integral double ribs, allowing axial positioning of the needle roller assembly in both directions. The inner ring provides a standard raceway and can be installed directly without requiring shaft surface hardening or grinding, reducing associated costs.

Extreme Compactness: The radial height is much smaller than that of deep groove ball bearings or cylindrical roller bearings. Load capacity is increased by 30%–50% within the same installation space, making them ideal for confined layouts.

High Load Rigidity: With numerous long and thin needle rollers and large contact areas, they feature outstanding resistance to deformation and eccentric loads under pure radial force, suitable for heavy-duty, shock, intermittent, and oscillating conditions.

Easy Installation: With a standard inner ring, the shaft requires no special hardening. Both press fitting and thermal fitting are applicable, and the separable structure simplifies assembly and maintenance.

Stable Precision: Machined rings plus precision cages ensure high rotational accuracy, low friction, and low temperature rise, adapting to continuous medium-to-high speed operation.

Optional Sealing: Available in open type, double rubber seals (2RS), and dust cover types to accommodate dusty, oily, humid, and other complex environments.

2. Model Classification and Core Selection Criteria

Main Model Series

NA49 Series (Standard Thin-Wall Type): The most widely used, with the smallest radial cross-section, suitable for light-to-medium loads and medium-to-high speeds (e.g., NA4900, NA4905, NA4910).

NA69 Series (Extended Thin-Wall Type): Greater width, higher load capacity and rigidity, ideal for heavy loads and long shaft supports.

NA48 Series (Ultra-Thin Wall Type): Extremely low radial height, designed exclusively for ultra-compact space applications.

Double-Row NA Series: Dual needle roller rows with doubled load capacity, suitable for high-shock and high-rigidity demands.

Key Selection Factors

Load: Primarily pure radial load; cannot withstand axial forces. For heavy loads or shocks, choose double-row or full-complement NA bearings; for light loads, standard NA49 series is recommended.

Space: For radial constraints, prioritize NA48/NA49; for axial limitations, select narrow-width types; for high rigidity, use NA69 or double-row versions.

Speed: Oil lubrication supports higher speeds than grease lubrication. For high speeds, use caged and sealed types; for low-speed heavy loads, full-complement needle designs may be used.

Environment: For dusty or humid conditions, select 2RS sealed types; for high temperatures, use high-temperature resistant grease; for mild corrosion, stainless steel NA bearings are optional.

Shaft Condition: If shaft hardness is insufficient (<58HRC) or grinding is impractical, NA series with inner ring must be used. If the shaft is already hardened and ground, RNA series without inner ring can be applied to further save space.

3. Typical Application Scenarios

NA series bearings are widely used in equipment requiring compact design and high radial load capacity:

Automotive: Gearboxes, differentials, steering gears, engine accessories, oil pumps, camshafts, connecting rod mechanisms

Industrial: Machine tool spindles / turrets, reducers, hydraulic pumps / motors, textile / printing / packaging machinery, power tools, conveying equipment

Construction Machinery: Small winches, hydraulic valves, traveling mechanisms, oscillating joints

Others: Medical devices, robot joints, precision instruments, household appliance transmission parts

4. Installation, Lubrication and Maintenance Standards

Installation Guidelines

Tolerances for shaft and housing bores: Use standard fits (shaft h5/h6, housing bore H7/H8) to ensure coaxiality. Forced hammering is prohibited; press fitting or thermal fitting is preferred.

Inner ring fixation: Use interference fit or shaft shoulder / retaining ring positioning to prevent axial movement. Press the outer ring into the housing bore to ensure end-face contact.

No axial preloading: NA bearings only support radial forces. Axial loading will cause needle roller jamming and rapid wear failure.

Lubrication Requirements

Lubrication method: Grease lubrication (general use) and oil lubrication (high speed / high temperature). Fill 1/3 to 1/2 of the internal space to avoid overheating caused by excess lubricant.

Grease selection: Lithium-based grease for general use, complex lithium / polyurea grease for high temperatures, low-pour-point grease for low temperatures. Regrease periodically (every 1–3 months under normal conditions).

Troubleshooting and Maintenance

Abnormal temperature rise / noise: Mostly caused by insufficient lubrication, excessive tightness, poor coaxiality, or contamination. Stop immediately for inspection, cleaning, and regreasing.

Needle roller wear / jamming: Commonly caused by axial force, lubrication failure, or overload. Replace the bearing promptly to avoid damage to the shaft and housing.

Seal failure: Inspect seals regularly and replace immediately if damaged to prevent dust and water ingress.