The method involves forming a spine (3) of a U-profile in a sheet metal bank. A side piece of the U-profile is bent around 90 degrees. Another side piece of the U-profile is bent such that it lies parallel to the former side piece. The bent side pieces are perforated at ends of the side pieces, and edges of holes are formed outwards under formation of collars (4c, 4d, 5c, 5d) with internal bearing support surfaces (4e, 4f, 5e). The holes are gripped in the side pieces by hollow and form tools and are guided by the tools.
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