How to add a column with Featured Thumbnail to wp-admin

How to add a column with Featured Thumbnail to wp-admin without using plugins.

You can specify the size of the thumbnail using the_post_thumbnail().

add_filter('manage_posts_columns', 'posts_columns', 5);
add_action('manage_posts_custom_column', 'posts_custom_columns', 5, 2);

function posts_columns($defaults){
    $defaults['show_post_thumbnail'] = __('Thumbnail');
    return $defaults;
}

function posts_custom_columns($column_name, $id){
	if($column_name === 'show_post_thumbnail'){
//         echo the_post_thumbnail( 'thumbnail' );
        echo the_post_thumbnail( array(50,50) );
    }
}