Carl,
Here are photos of mine. Now, while I have several reasons to believe this is a very real and correct cap for the '57 Chrysler, there are others who may prove me wrong. I bought the car in 1962 with an identical cap on it, but I did not see it when it was brand new.
The interesting thing to me is that even though there is no little hole in the middle of it, it is pretty clearly stamped "VENTED". I did not take the time today to figure out just where the path of the venting air runs. Wait, I think I see it. The expansion air travels out through the hole in the inside center cone, travels over the filler tube gasket, and then exits through the two grip bumps. That would be the reason for the two "dashes" that are stamped into the cap surface.
Are there other '57 owners with this cap, and who share my opinion that it is a correct original?
Thank you.
Keith Boonstra
PS -- my apologies for showing up in the selfie cam here, but it was my only solution. Dropped my phone today, and now the backside camera of my IPhone will not focus clearly and I had to do my best using only the front camera.
PPS -- usually cameras are known to lie on the good side, but these shots sure do make the paint in my filler cap area look pretty tacky. Now I'll have to fix that up.