Worried that the new rotary evaporator you're thinking of buying doesn't fit your existing glassware? You don't need to be! Instead of having to buy all new flasks, you can simply use glass bushing adapters. They convert one glass size to another and allow you to use evaporation flasks with a glass size dissimilar to that of your rotovap's joints.
Most general-purpose laboratory glassware manufacturers who make jointed glassware will also make bushing adapters, and a quick internet search should come up with plenty of suppliers.
a series of glass bushing adapters
