seven sided coins

April 25, 2024 12:02 AM

An Alphabet of Heptagons: Seven-sided Coins [See also: Polygonal coins]
posted by dhruva (7 comments total)

More accurately, most (all?) of these are Reuleaux heptagons, and are shapes of constant width. This allows them to roll through coin-operated machinery without getting stuck. Many of those in the second link are just conventional polygons, but having more sides (e.g. 9) makes them more 'round', mitigating the issue a different way.
posted by pipeski at 2:27 AM on April 25 [3 favorites]

I still have a soft spot for the Susan B. Anthony dollar, a much unloved coin that, while round, faked it with an eleven-sided internal cut design.
posted by chavenet at 3:04 AM on April 25 [3 favorites]

pipeski, came to say that. Curves of constant width are fascinating, and are an alternate solution to the "why are manhole covers round?" thought experiment* since, using those curves, there are in fact 3- and 5-sided manhole covers. And the 3d-printable solid shapes of the same are just crazy to play with.

(* but only a solution to the part about them not being able to fall into the hole. There are other reasons that also add in to why they are most commonly round)
posted by mystyk at 3:29 AM on April 25

"...but all were opposed by the vending machine industry, a powerful lobby affecting coin legislation."

well known to have influence in almost every lobby in the nation
posted by phooky at 4:39 AM on April 25 [10 favorites]

This was surprising and educational for me, since I had no idea that all those small UK-linked territories, like the Falklands, had their own coinage. I was also surprised to see that the unit of currency in the Seychelles is the Rupee.
posted by adamrice at 5:47 AM on April 25

These photos are sooooo perfect. So much detail and perfect lighting. I'd love to read about how they were photographed.
posted by cccorlew at 6:30 AM on April 25 [1 favorite]

The Canadian loonie is an 11-sided Reuleaux polygon.
It's dimensions , weight etc are almost identical to the Susan B. Anthony dollar coin
posted by yyz at 1:46 PM on April 25