Here is my Autolite 4100 as installed on my 1968 Cougar XR7. Cast into the body on the driver side of all 4100 and 2100 carburetors is the venturi size. You will see lots of sizes on the 2100, the 4100 will be 1.08 and 1.12, that rare (1.19) one that Terry mentioned, is the Holy Grail so to speak. The one shown in the picture is a 1.12, but I sent it to Pony Carburetor and they rebuilt it with their 'spreadbore kit'. They installed a reducer on the primary side that measures 1.00". Poke around on their site for the details.
DUH! I get it now. It's gone through the first two layers and slowly making it's way through the next two or three. Yes! We have comprehension.
