the single- and double-flange edge
The Breen & BB Encyclopedia of early date cents mentions single- and double-flange edge varieties on page 438. You can't hunt for them at shows because the coin edges are usually hidden. They're never mentioned in auction catalogues. Presence of them in our collections may therefore be entirely random.
I'm wondering how rare these are and who else in CN can report owning one or more, on which varieties, and at what rate do they occur in your set?
I have four: s212 and s236 with SFE and s239 and 32 N2 with DFE. That is 4 in 630--rather rare!
Here's a couple of pics00 s212 SFE.jpg02 s239 DFE.jpg
What is the cause of this effect?
apparently done by an "upsetting machine" used on some planchets. More info is on page 369-372 of the Breen & BB encyclopedia.
Just realized my 1803 C4 also has a single-flange edge.