Judging by the bottle bosses on the understide of the seat tube I am assuming it is a touring frame yes? What brand?
I would bet it is for a generator set up of some sort. But also as mentione it could even be for a fender perhaps from the maker of the frame.
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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