I have one of each from brewershardware. The 2" is bigger width. You cannot put the 2" on the 1.5" tube. I used a sight glass for a yeast harvester as well but changed. I start with the sight glass to know when to drop trub. Then I take it off and just dump from the bottom port into sterilized mason jars. Way more yeast is produced than what will fit into a sight tube.