Here you have some better pictures of the C1 chair from 1959. This very chair was likely from the Plus Linje / Unika Væv exhibition at Möbel Phister in Zürich 1961. There is a famous black and white picture from there. The small metal piece under the cross foot was put there by Plus Linje because they were not sure the cross foot would hold the pressure of this heavy chair. The chair has a steel body inside and weights a lot more than you first think.