So, I just picked up a couple of glass carboys from CL. A 5 gallon and a 6.5 gallon. I'm familiar with 5 gallon carboys, but have never actually seen a 6.5 in person. That's why I'm not sure if what I have is standard or not. Are the openings on the 6.5s smaller than their 5 gallon counterparts, do they all have a screw threading on the neck of the carboy?
I'm asking all this because I want to buy a carboy cap online, but want to ensure it will fit.