Post caps are not something you think about every day, but they are necessary for fences that include fence posts. Post caps can be wood, metal, or plastic. Some are designed for gate posts, others for fence posts of other types.
Post caps sometimes come in decorative shapes resembling chess pieces, flowers, human heads, or abstract designs. Others are more utilitarian, simply a square or rounded piece to fit on top of the post and keep the fence rails in place.