Originally Posted by
majmt
Big frame……..might be for mounting a frame-pump support bracket beneath the top tube. Just a WAG.
Back in the late 80's I remember putting some under the top tube water bottle bosses to hold a short Blackburn pump that had a holder designed for those under the top tube bosses. I don't think Blackburn made that holder for long. They went to holders that could fit on the side of a water bottle cage but was held in place by its bosses..