IIRC, they are mounted with 2 metall clamps that are screwed to the instrument holder. See:
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As aluminium is rocketing in price it will not stay at this price for very long. It is supplied with stainless studs and nuts as shown. The item is supplied in satin finish so that you can paint it or get it polished.
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all 3 screws need to come out, but at least the top one (the others can be just losened, so you can move the metal strap enough to take the instruments out)