12 x 21 x 5 mm Hirobo HI2500047 Shielded Ball Bearings, 2 pcs  [HI2500047]

Precision 12 x 21 x 5 bearings for hobby gearboxes

This item contains two Hirobo 12 x 21 x 5 mm shielded ball bearings supplied as a pair. They are intended as spare or replacement bearings for compact rotating parts in small scale RC projects.

These shielded steel bearings are chosen where space is tight but reliable rotation is needed. Fit locations commonly include small drive shafts, tail drive components, and gearbox supports where the 12 mm bore and 21 mm outer race align with the existing mounts. Always double-check measurements before installation.

Recommended fitting method: use a press or a bearing driver that contacts the outer race at the 21 mm diameter to fit the bearing without stressing the inner race. Avoid pressing directly on the inner race when installing on a shaft. For removal, employ a proper puller or apply controlled heat to loosen a tight press fit.

Preventive maintenance: clear any debris from the seating area, consider a light protective lubricant only if compatible with the shield, and inspect the shields for wear. Low-friction bearings help keep drivetrain backlash minimal and improve smooth operation.

Storage tips and replacement cues: keep bearings sealed in dry containers and replace them if you detect rough running, increased endplay, or noise under load. Inspect bearings regularly after intensive use.