Pex Fittings Flair It Bulk, Flair-It Couppng 3/4'. Connects 3/4' Pex Or Polybutylene. When Connecting 3/4' Polybutylene With This Fitting, Always Use Part # 06792: 3/4' Pex To Polybutylene Transition Insert. The Wall Of 3/4' Polybutylene Is Thinner Than