Picket collars or knuckles are a cost effective and easy way to jazz up plain pickets that will be used in metal staircase railings, fences or gates. Many styles are offered in steel, aluminum and brass. Collars are available for both round and square bars with the 1/2" sq. or 1/2" dia. size as the most common size. Collars are also available to fit over 9/16" to 1-1/4" should the design call for a larger material.