The steel mill he bought in 1989 was part of Ford's great River Rouge plant, where the father of mass-produced cars turned raw materials into vehicles on a single site -- transforming ore and rubber into finished cars (see box, p.122).
Some say, it was the side-by-side placement on the printing press, some say the pockets in the wallets were the limiting factor, there is some limited indication that the card size was to match the pocket tobacco box to which these cards were held with a rubber band.
Finishing things off: 2 millimeters of lining leather, Vibram rubber soles, a steel shank, a leather heel counter and a styrene toe box to harden the front and prevent nasty stubs.