Hirobo HI2521123 4 x 5 x 4.3 Shaft Collar for RC Helicopter Fitment  [HI2521123]

Helicopter shaft collar function and fit

The Hirobo HI2521123 collar is an accessory marked by its part code and dimensions, intended to locate and keep parts in place along a model helicopter shaft. Acting as an axial spacer or stop, it helps bearings, gears and linkages retain their designed positions during operation.

Fitting is direct: place the collar where axial registration is required and secure using the model's retention method or a compatible fastener. Because shaft profiles vary across kits, confirm the collar clears rotating components before final torque is applied.

For maintenance, collars play a role in controlling endplay and preserving gear mesh. Inspect the part regularly for wear, corrosion, or deformation and replace it if you notice persistent movement that could affect axial control.