€¢ Create a straight course in masonry €¢ Work on various size blocks from 4 inch - 12 inch €¢ A wing nut makes it easy to change size €¢ Strong aluminum construction >> Stretch mason's line between course blocks for straight walls. Sturdy; lightweight aluminum line stretchers work on various size blocks from 4 inch to 12 inch. Change the size by moving the wing nut to appropriate size. Sold as a pair."