The EO-2 progressive ring fitting is a Parker flareless fitting for metric tubing similar to the EO series. The difference between EO fittings and EO-2 fittings is the additional elastomeric seal (on EO fittings), which provides leak-free operation without re-tightening - even under severe conditions.
Another difference is an EO-2 functional nut, which incorporates both the ferule, and the elastomeric seal. The EO-2 functional nut simplifies the EO-2 connection assembly.