Hirobo HI2521124 12 x 15.9 x 6.8mm Helicopter Shaft Collar  [HI2521124]

Axial spacer for rotor assemblies

The HI2521124 collar by Hirobo is a compact spacer sized 12 x 15.9 x 6.8mm, intended to control shaft spacing in helicopter builds.

Installed as a positional locator within rotor heads and gear stacks, the collar helps retain concentric alignment and reduce endplay under load to stabilize rotor dynamics.

Installation guidance: press the collar onto the shaft, ensure it contacts the adjacent component fully, inspect for ovality before reuse, and secure it according to the original assembly method.