These were all sold in mm sizes.
One inch meaning the smallest, 1-3/4 the second and 2" the largest.
Compare a 1-3/4" to a 2" and be surprised.
Back in the day the when the 1" were sold @ToysRus there may have been an ad to send in and get a larger one, I have never seen this ad.
I still believe it to be true though and would love to see one if any help is out there.
The marbles were also (imho) sold at glass shops in the Old Malls.(no proof yet)
This is where the paper/advetisement above in this post came into play with this type.
I have measured true Atmos @just over 7/8' and just under 1-1/16".
Marble--On!!