Closed dies can be used to forge specific shapes in ferrous and non-ferrous metals. If you use a larger bar than 1/4 inch this die will produce flashing (excess metal squished out the sides) which extends beyond where the tenon metal is. If you twist that tenon with flashing this is what it will look like. Use 1/4 inch round stock to make this tenon. The closed spring die used to make this is the product you would be buying, not the tenon itself.