This heavy duty boss head is die casted alloy that has been painted gray. It has 2 metal adjustable metal thumb screws accepts rods up to 19mm in diameter at a right angle to one another. Metal thumbscrews allow for adjustment and to secure rods in to position. This heavy duty boss head is die casted alloy that has been painted gray. It has 2 metal adjustable metal thumb screws. It accepts rods up to 19mm in diameter at a right angle to one another. Metal thumbscrews allow for adjustment and to secure rods in to position.