This winch post cap is sized to fit angled 2" x 4" boat trailer winch posts. The winch post cap helps prevent saltwater or corrosive elements to get inside of your winch post, keeping the interior of your post from rusting. The rubber cover can also help protect yourself and others from potentially catching the abrasive edge of the winch post. This cap is only compatible with angled 2 x 4 winch posts, it will not work on a vertical 2 x 4 post.