Sheet metal shaping machines smooth, curve, and stretch metal workpieces. They are commonly used to form and finish domed workpieces. Power planishing hammers shape and smooth metal by striking it with forming dies. English wheels add curves and contours to sheet metal as it rolls back and forth between two anvil wheel dies. Shrinker stretchers use their clamping jaws to either contract sheet metal to form inside curves or expand it to form outside curves.