Inertia weights are small "extra brakes".
They increase the gyroscopic stability of the flybar and slow down the rotor head's response.
For every beginner we recommend these so the responsiveness of the rotor head is reduced. The rotor head becomes more responsive as the inertia weights are moveded inwards (always place equally!).
Inertia weights suitable for 5mm flybars; complete set for one rotor head, including hardware.