Calibre 3220 winding - Speedmaster Automatic (Reduced)

JimInOz

The mainspring in a manual wind watch is held at both ends, the inner by a hook on the arbor and the outer has a hook that engages in the wall of the mainspring barrel. When the watch is fully wound, the mainspring is held at both ends by the hooks and can be wound no further.

An automatic mainspring is held by the hook on the arbor, but the outer end is a smooth curved heavier spring called a bridle. It doesn't lock to the barrel but will slip when spring coils are wound around the arbor, lessening resistance at the outer coils. The barrel wall is lubricated with a grease that holds the bridle up to a certain load point, then breaks and allows the bridle to slip until the spring coils expand slightly and the grease brakes the bridle. thus the reason the grease that breaks is called braking grease.

In theory, an automatic can be wound indefinitely, the amount of resistance approaching full wind will depend on the strength of the spring/bridle, condition of the barrel wall and the type/amount of braking grease used.