no specific measurements but most steel Bianchis from the mid to late '90s had that larger ovalized DT. vertical at the top then sort of becoming round in the middle then horiontal at the bottom. there isn't anything stamped on it?
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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