I'll have to check my "new to me" Rossin and see what it has. I do think I have seen them on other nicer Italian frames. I guess the idea is to stiffen the stays without a bridge and thus make them shorter?
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk