The invention provides a thermal fin structure, and a method and apparatus for forming a thermal fin structure, which is effective in minimizing frost bridging in refrigeration operations. The thermal fin structure is wound helically onto a refrigerant-carrying tube, and comprises an integrally formed chain of looped fins, each looped thermal fin having a mounting flange at each end thereof and comprising two vertical thermal fin portions extending respectively from each mounting flange and connected together by a bridge portion; the method and apparatus for making the same includes a unitary stretch preforming process to reform thermal thin lanced sheet metal fin stock into the thermal final looped thermal fin shape in a single forming step. |