The weathervane pillar is a quest item used in the One Small Favour quest. It is obtained by climbing onto the roof of Phantuwti's house in Seers' Village and removing the broken vane parts. The pillar must then be repaired using a steel bar at an anvil and returned to the top of the house, along with the repaired directionals and ornament.
Once the three repaired vane parts have been returned to their position, the player can speak to Phantuwti in order to complete the next step in the quest. It can be discarded afterward, as there is no further use for it.