Broken weathervane parts are a quest item used in the One Small Favour quest. They are obtained by climbing onto the roof of Phantewti's house in Seers Village and examining the weather vane there. Each part must be repaired using a different metal bar - the ornament on top must be repaired with a bronze bar, the directionals need an iron bar, and the weathervane pillar requires a steel bar to repair.
Once repaired, the parts can be returned to their position on top of the house in order to continue with the quest.