A bicycle
seatpost,
seatpin,
saddlepole,
saddle pillar, or
saddle pin is a tube that extends upwards from the
bicycle frame to the
saddle. The amount that it extends out of the frame can usually be adjusted, and there is usually a mark that indicates the minimum insertion (or maximum extension). Seatposts can be made of
steel,
aluminum,
titanium,
carbon fiber, or aluminum wrapped in carbon fiber.