Well my Google Foo failed me today.
Fella at work drug in 2 old railroad lights he bought on Ebay. I think they may have been to tell whether the track switch was thrown. I don't think they originally had a light inside, but I am rigging a single bulb socket in them for electrification. The glass lenses he was given/sold are NOT the right size and it will be cluster xxx to use them. The OD of the lens holder is 5 1/4", 5" might work.
I have entered all kinds of things in Google and get lots of eyeglasses. Trailer and car sites show round lenses, but I've not found any that tell me sizes. Glass would be best. Each light needs 4 lenses - 2 red and 2 green (the colors are a guess, but that is what he was given). I suggested a modification to the sheet metal to use the lenses he has, but he doesn't want to modify the original Atchison Topeka and SF units.
If anyone has any sources or info it would be appreciated.