Steel edge rotary hemming units are suited for hemming a steel leading edge on the copper fin. It gives core strength to copper cores by adding a steel leading edge. It is used to roll form a hem or turn-up on the edge of the fin. A set of pinch rolls pull the material through the machine and are operated by a dancer arm controlled motor. This motor runs at the same speed as the fin machine. Its center trap plates are used to hold the material in place as its being hemmed.