< I do not know for sure how Duprat cranks were made hollow, but my guess is that they went through an initial forging process, then the arm was drilled, then the crank was subjected to a final forging process in which the open end was closed up and shaped into its final form and drilled and tapped (assuming that it was drilled from the pedal end). This way it is all one piece, no assembly involved.
Bugatti similarly mystified people with his beautiful one-piece forged hollow front axles. In this case they were forged straight, drilled through and then final shaped.
Hugh Thornton Cheshire, England>
That is how I figured they were made except that they would have been closed up from the crank end, the round hole being formed into the slot at that end. I wonder why they wernt to so much trouble; they were not charging Ettore Bugatti prices. Stuart Tallack in West Sussex