The striking face has teeth in a swirl pattern, which grab the stretched metal. When you strike with the hammer, an internal cam rotates the head for faster shrinking action. Bonus for repairs on newer cars, since you should not heat high strength steel above 700 degrees F, which rules out traditional in.torch then quenchin. shrinking. The fast action will help save time and money on bodywork. Top quality German coachbuilder's tool, made for professional bidymen. Made in Germany.