Hirobo HI2500047 Ball Bearing Pair 12 x 21 x 5 mm, Shielded Steel  [HI2500047]

12 x 21 x 5 mm shielded bearings for RC applications

This listing is for a set of two Hirobo ball bearings sized 12 x 21 x 5 mm. These shielded steel bearings are supplied as 2 pcs and serve as direct replacements or spares for compact rotating assemblies in hobby models.

Compact shielded bearings like these are often fitted where a low-profile solution is needed to support shafts and gear trains. Common installation points include small main shafts, tail rotor assemblies, and gearbox positions where the 12 mm inner diameter and 21 mm outer diameter match the host part. Verify dimensions before fitting to ensure correct seating.

Fitting advice: press the bearing in squarely by applying even force to the outer race or use a bearing driver sized to the 21 mm outer diameter to avoid loading the inner race. Do not push on the inner race when mounting to a shaft. For extraction, use a puller or apply controlled heat to the housing rather than levering on bearing faces.

Care and tuning: remove debris around the mounting area before installation, use a light hobby bearing oil only if the shield design allows penetration, and inspect the shields for damage. Smooth bearings reduce drivetrain lash and can improve control feel in rotor and gear-driven systems.

Storage and service: store bearings dry and dust-free, and replace them if you notice roughness, excess play, or unusual noise under load. Check bearings periodically after heavy use or if vibration increases.