Set of 16 keys. For use with the Masterpiece K3 Heavy Duty Stretcher Bar. This key or wedge is made from 5 ply birch plywood and is designed to insert into the inside perimeter of the frame into the little slots of the Stretcher Bar tenon. Use these keys to increase the tension level of the canvas. By inserting the wedges and lightly hammering on the keys, the frame will enlarge and thereby increase the tension on the canvas. We recommend the use of this product only when the canvas is loose and needs to be tensioned.