Why would the gold plates be bound by the most efficient ring shape?

Multiple witnesses said that the gold plates were held together by three D-shaped rings. If Joseph Smith had made the plates himself wouldn’t he have likely used circular rings? Why would he go to the extra effort to make them D-shaped?

Jeff Lindsay explains:

…a ring with a straight side is more efficient for holding stacked plated or sheets than a purely circular ring. In retrospect, it makes sense that experienced users of metal plates would use an efficient binder system. Warren Aston reports that the D-shaped ring “offers a full 50 percent more storage capacity than a circular ring” and “20 to 25% percent more storage capacity than a slanted semicircular shape,” though details of the calculations are not given (but it sounds reasonable).
– Jeff Lindsay – A “D” for Plausibility of the Gold Plates: The Book of Mormon in an Interesting Bind

Lindsay continues:

Joseph Smith displayed plates that were securely bound by three rings (not two or four) constructed in what we now know is the most efficient shape. He could not have known either of these facts in 1829 from the materials in his environment or from people who may have had greater familiarity with libraries or materials storage. Nor could he have been informed by the finds of other ancient records, as none were then known to be bound by rings. Perhaps it is not coincidence that the only other ancient record bound by rings so far known also has D-shaped rings and dates to about 600 B.C.
– Jeff Lindsay – A “D” for Plausibility of the Gold Plates: The Book of Mormon in an Interesting Bind

How did Joseph Smith know about D-shape rings when patents for this design were only made after his time?

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