FELLOE (RIM BASE)

In horology, the felloe (rim base) refers to the peripheral ring of a wheel or a Balance — also referred to as the Rim —, that is, the outer circular part that connects the arms (or spokes) to the central hub. On a toothed component of the Train (wheel train), it is generally on the edge of the felloe (rim base) that the teeth are cut; certain old mechanisms with pins, notably in striking trains (pin wheel), instead attach their pins directly to the felloe (rim base) rather than cutting teeth into it.

On the balance, a component lacking teeth, the felloe (rim base) forms the outer ring bearing most of the Mass and connected to the Axis by two or three arms. It is on this ring that the regulation screws or weights are arranged, allowing the Inertia of the Regulating organ, hence the Daily rate of the watch. In old bimetallic compensation Balances, the Felloe (rim base) itself was cut at two points near the arms: the composite Blade (Brass on the outside, Steel on the inside) would then curve under the effect of Temperature, thus correcting rate variations linked to the Expansion of the Hairspring (balance spring).