Rosedale Iron 1/2" › Adjustable Knuckle Image 1 of 1 Adjustable Knuckle $0.00 Designed for 1/2” square balusters. An adjustable knuckle collar with set screw can be place at any height on a baluster. Add To Cart Added! Designed for 1/2” square balusters. An adjustable knuckle collar with set screw can be place at any height on a baluster.