An adapter is for use in cooperation with a post. The adapter includes an upper adapter portion which will be attached to a first part of the post, and a lower adapter portion which will be attached to a second part of the post. The adapter also includes a cylindrically helical spring connecting the upper adapter portion to the lower adapter portion so as to allow relative movement between the upper and lower adapter portions, including either rotational movement in which the post remains upright, or movement in which the first part of the post bends, or both. At least one of the two adapter portions is shaped to receive the helical spring as a screw.